It certainly is a pacing mechanism, but it's also something that, in part, drives my decisions when playing. I play in three games and DM one game. The three games are sandboxy, though the size and focus of the sandboxes varies a bit. Each one handles XP differently.
In the desert hexcrawl, we get XP for combat only, so we tend to beat things up a lot and take their stuff. Social only comes up when we think it might be amusing or puts off a tough challenge until we're in better shape to tackle it (then inevitably betray and kill them later).
In the West Marches style hexcrawl, we get XP for combat and for quests. So we choose the quests that will net us the most XP for the least amount of effort and fish for random encounters as much as possible between town and the quest location. I played in this one last night and went from 4th to 5th level in about 3 hours.
The third campaign is more of a town-to-megadungeon type setup, but we get XP more like Dungeon World End of Session move. The DM asks some questions and we have a conversation about it and get XP that way. One of the questions is "Did we battle any notable monsters?" The impact on play is that we don't actually seek out combats with as many things as possible like in the other two games, but rather just one notable thing then we're good (at least where that question matters - there are others).
So I guess whatever method you're using, consider what sort of play it's incentivizing because it will tend to have an impact on what your players actually do in your game. Story-based advancement incentivizes sticking to the prepared plot. It's not that great for games that don't have a plot. Session-based advancement incentivizes just showing up regularly and doesn't really incentivize playing any particular way. And so on.