I used VTTs for a long time before using dynamic lighting. I didn't want to fiddle with tracing walls, doors, etc. When I played with it on Roll20 performance was bad.
For in person games I used Realmworks with the player view displayed on a horizontal display. It had great tools for the DM to reveal areas and revealed areas stayed revealed. I didn't see the need for dynamic lighting. When I went online and needed to display tokens, I went with Map Tool, sharing the map via Google Hangouts. I just used Map Tool to quickly search through my hundreds of maps and tokens and set things up with Fog of War which I would manually reveal. It worked okay. I never so the need for anything more.
But Foundry has converted me. Tracing walls and doors are simpler than in any other tool that I've used and the line of sight experience for players and DM is excellent.
In my experience, and based on player feedback, it really adds to the experience. I'm currently running Rappan Athuk, which is a massive mega-dungeon. In other campaigns I don't know that I would prep every map with lighting and line of sight, but it really adds to a dungeon crawl.
To address some questions and detractions raised by other posters:
1. In Foundry, you can use progressive reveal so that explored areas stay revealed. When not in line of sight, they will be a bit darker but still revealed. I used to require that at least one character in the party have cartography skill to enable this, but its become something the players expect and like that I just assume that all adventurers have decent mapping skills.
2. I like how it makes different characters dark vision distances mean something and lighting sources are important. The deep gnome will see further on the map than the dwarf. The human will need some light source. In theater of the mind, tracking and determining lighting resources or remembering to take into account how far different characters can see in darkness feels like a chore or is something easily forgotten or generally fudged as I juggle everything else I have to do as a DM. The deep gnome looses that differentiating characteristic when I'm not using lighting and line of sight. It is nice to have the VTT take car of that for me.
3. Regarding players running ahead. We'll, if they move over a trap, that's on them. But I get your point. There have been some spoilers when I started using line of sight and lighting when I first started using it instead of manual fog-of-war reveal. But Foundry has a number of features that help with this, which has kept this from being a problem.
- First, I can "pause" the game at any time by hitting the spacebar and unpause it by hitting the spacebar again. This makes it easy to stop character from going around a corner if there is something that should happen before the do, or if I need a moment to react, etc.
- Second, you can set doors as "locked" so that characters cannot open them until you unlock them. Having all doors as locked can also help prevent players from accidentally clicking on them opening them.
- While in combat, you can prevent a player from moving his or her character's token until it is that character's turn.
4. As for the extra prep time. That was what stopped me from using these features at first. And, when I did start using them, it DID make prep time take longer. But now that I'm used the software I find it has reduced my preptime because prepping the map more effectively familiarizes the map for me than just reading and reviewing it in a book or PDF. Also, I make sure to have the monsters places so I'm familiarizing myself with the likely encounters. I'm placing notes about traps etc. It makes the game run a lot more smoothly when I have the maps prepped in my experience. So overall, I don't think the prep time is onerous.