I'm not a completionist - they simply want to experience every part of the game.
I'm someone who is an "efficitionist" - huge difference. It means that I want my character to be as good as can be if possible. If there's extra XP to have with a limited XP in total, I'll want to get it and feel crap if I don't. Same with items: if there's items I need or could use well, I'll want them.
With games like DX:HR, I want to tackle problems in the most efficient way as well - if I notice stealth would be more appropriate in one location, I'll want to use it. In the next room, I might find that combat is more efficient in tackling the situation. Because of this, I need to have enough XP to make me good enough in both to be able to do that. Stuff like breaking through walls and shit, were pretty much a "must" for me and there were quite a few such skills that I wanted quickly.
In short, games that offer limited XP yet make you focus on certain skills will ALMOST make me want to squeeze every XP point out of it - and in DX:HR you could get a LOT out of hacking everything you can, including alarms.