You know KM I have to say, I don't agrre here, and after thinking about it for a while...here's why. Improv isn't something anyone can do, that's why some people do better on timed tests than others, even though their knowledge and skill level are the same.
I'll be happy to explain.
It's a skill, and like any skill, it gets better with practice. Anyone who can think sitting down can think on their feet, it's just a matter of getting used to it enough to be comfortable with it. There are improv classes available in any city with an acting population, and a lot of the rules for stage apply to gaming on the fly, too.
Some people do better on timed tests than others, but those who don't do well can always improve their performance.
Another thing is ramifications, I feel that steadily improv'ing is akin to lying(not in a negative way) in the essence that it's too easy to "weave a tangled web" that when looked at closely makes no sense or has various inconsistencies(unless you have a memory like a super computer),.
Maybe you're just not a very good liar.

It's really easy to have a few basic archetypes and hang weave a web around those. You create information as needed, just making sure it doesn't contradict what has come before. So as the PC's examine (say) the elven tea ceremonies, elven tea ceremonies become deeper and more significant, but very little time is spent on the Necromancer King.
A good liar, much like a good writer, knows when to be vague and let someone else fill in the details and figure out the inconsistencies.
Oh yeah, and if you're writing it down then aren't you just doing twice as much, or at least an equal amount of work when compared to writing it out beforehand?
Not really, since you're just taking notes on the experience. That's quite a bit less work than the Sisyphean quest of trying to extensively detail every direction the PC's can go, I think.
In his oppinion it is way more demanding than doing scripted comedy. The question I pose is for a DM whose having fun what advantage does a more demanding playstyle have over one that's less? In other words...if my purpose is to make you laugh then what is the "advantage" to more stress, uncertainty, and workload? It's great that YOU enjoy this style and have the skill set to make it work, and I highly respect my friend for having those skills as well, but just like they're are some people who lack dexterity, or just aren't funny...they're are people who aren't good at improv and no amount of practice will change that.
I wouldn't advise people to accept the total improv campaign whole-heartedly, any more than most people would advise a new DM to write a 256 page World Setting bible before they begin. Most campaigns are going to have a nice middle ground between the two, and most DMs will balance whatever improv ability they have or acquire with whatever writing ability they have or acquire.
But I do think that the idea that a deeper and richer and "better" campaign setting requires more writing and pre-preparation is a notion that must be disabused. More preparation doesn't necessarily make your world deeper and richer than mine. It has no inherent advantages. Improv doesn't have any inherent advantages, either. They are different ways of getting to 4. A 256 setting bible might be 4 + 0, total improv might be 0 + 4, most campaigns might be closer to 3 + 1 or 2 + 2, or 888 + -884, or whatever. It is much more important to show DMs how to use the abilities and interests they have, rather than to tell them they'll need to do hours of extra-game work for the slightest in-game payoff when it really isn't true. They only need to do the extra-game work they enjoy.
I agree with this statement. But you seem to be extending it to a further idea that I don't agree with. That would be that there is no advantage to world building in and of itself.
It is true that good improv alone is all it takes for a great game.
But it is not true that improv and prep do not offer synergy.
Further, a given DM's improv ability at a given session is fixed. They may get better over time, but at the table their skill just is what it is. Background prep adds some non-zero value. The magnitude will depend on how good the DM is at building solid stuff that fits the on-going plot. But there is some addition that will add on top of the improv ability of that DM, be it awesome or terrible.
Background prep can add a lot of zero value, actually. 256 pages of 0 value.
HOWEVER, my own way of doing things is just as extreme as a 256 page setting bible way of doing things, so most DMs will find a comfortable middle ground for them. Some total that adds up to 4.
There is no inherent advantage to worldbuilding. But some DMs like it and use it just fine. There is no inherent advantage to improv. But some DMs like it and use it just fine. And each method creates fairly equivalent campaigns, so like in my original post, you *don't* need to spend countless hours crafting your campaign setting. There is, in fact, no inherent virtue in doing so.
However in the end, we players realised that we were just that - an audience. The lack of preparation meant that there was no illusion that the world existed beyond whatever the GM was making up on the spot. We weren't interacting with a world, just with the GM. These campaigns lacked the substance of those whose worlds exist beyond the immediate whim of the GM.
You describe the definite different feel of heavy-improv DMs, but that he lacked the substance just shows he didn't do it that well.
I've got as much setting material after my 8 hour D&D game as you have sitting in front of a computer writing for 8 hours, I just got it in a different way.
Ironically, I feel far more straightjacketed in improv games. I feel compelled to take whatever hooks the GM throws at me because there isn't an established wider world for me to explore. It makes me care a lot less about my characters because they aren't really a part of anything bigger.
A good DM builds confidence and trust and a living, breathing world. If you feel straightjacketed, it could be because the DM doesn't earn that from you. Regardless of the method used to come up with the hooks, this is true. If a particular DM fails to build that, you first have to look at them and see what they missed, and then look at yourself and see what demands you have.
My players invent their own hooks to explore, and go off into corners of the world that I then develop in response to their actions. My players delight in the feeling of being able to revolutionize an entire setting based on their actions, that the world moves in response to them, interested in what they're doing, who they are. The context for them is largely relevant to them.
It's a different feel, and it's not for everyone, but it still adds up to 4.