Whereas, for me, it's back to pacing.
When I ran the Savage Tide Adventure Path, my group would finish a module in about 6 sessions. Considering that the series is 12 adventures long, I was looking about about 70-80 sessions to finish the AP. For us, that's between 18 months and two years of gaming. Give or take.
IME, that's the absolute maximum half-life of a campaign. Anything longer than that is very much living on borrowed time, and most campaigns (heck, most groups) don't survive that long. I live in awe of people who manage to keep groups together for ten years. I do not.
So, adding in extraneous, irrelavent encounters actually actively works against me finishing the AP. Now, my goal as a DM is to never let a campaign sputter and die. I strongly want, both as a player and a DM, for every campaign to come to a satisfactory conclusion. That is one of my primary goals.
For me, adding in extra stuff that is not related to what's going on simply works against that goal.
To me, spending significant amounts of time, for example, on signposting encounters to create a "footprint" in the world comes far, far second to actually having meaningful events occur in the campaign. Because every time I spend time on irrelavent encounters is time I cannot spend on relavent ones.
As far as the "world" lacking a footprint, well, we've been over that ground far too many times. For me, the world can go hang itself. World building and mistaking setting for plot is the bane of fantasy. Fat, bloated, over written fantasy novels in desperate need of an editor willing to shave about 20% of the word count abound in the genre. I loathe world building and think it's a complete and utter waste of time at the table.
I do realize, however, that there are differing opinions here.
But, on a more serious note, I build campaigns with the presumption that I have a limited time frame in which to present a campaign. I no longer assume that my campaign will simply continue until it reaches some natural end. I can't make that assumption. Experience has shown that it never happens. What actually happens, again, in my experience, is that open ended campaigns collapse without ever resolving anything.
I simply have no interest in that anymore. Been there, and done that far, far too many times to want to do it again. Now, for me, give me a definite beginning, a tightly integrated group and a tightly woven storyline to interact with and I'm a happy player. Plunk me down in a fantasy world and say, "Go forth and find adventure, oh, you meet 1d6 orcs as you walk down the path." is pretty much the complete opposite of what I want in a game.