I feel like some people get a lot out of it, and others not so much. As in, if someone has the type of personality where they work best with lots of "heads-down" time on projects (and frankly many of the best engineers I know are like this), give them that space to do their best work without being interrupted by That One Person Who Always Comes Over to Chat. Most offices and even most orgs / teams have THAT DUDE. If you can't think of who it is, it might be you. Sometimes Dude has good ideas, but a lot of the time Dude just wastes time, and worst of all, wastes the time of others. Time that those other people could be spending Doing Work, but because Dude doesn't know when to can it, and because they're obligated to have their butts in their seats, they just make small talk while dying a little inside each day.

I've also seen people be incredibly productive because they can just walk over with a few people to another person and settle something in real-time. Doing that over email might take a day or two. Doing that over Slack could also probably work, and given how many people are in a meeting / out at lunch / OoO / whatever not at their desk, I'd say it's about a 50/50 chance that the unannounced walk-up actually works in person anyway.