I pretty much pick up just about anything and everything not nailed down in most RPG's.
It really depends on the game, though for what I do w/ them, afterwards. In most games, I will do lots of traveling and selling to item shops b/c they don't do some sort of salvage system like Two Worlds 2 - just to make that money and so I can buy more stuff.
Some games like Titan Quest, it just gets ridiculous - as some items are just worth garbage and I don't pick them up - and that game really litters you with items everywhere and they're worth crap on the sell. I think those were "gray" colored item.
DAO was interesting b/c you had the "destroy item" option. So, on-the-fly, if I had some items and didn't feel like travelling somewhere to sell them or store them, I'd just destroy them and make space and go about my adventures.
Two Worlds 2 has the best system, though. Destroy an item, get materials. Take materials - use them to craft or upgrade anything you want. So, I pick up anything and everything b/c they will yield materials once broken down. So, no - I often don't sell things off b/c of this. With a high crafting skills, you can really tweak out a stock item that's say Level 16 and give it a plus 6 Level upgrades by the time you trick it out (Level 16 + 6 item) - and essentially make it a Level 22 item w/ a whole bunch of sockets that you can put gems and stuff into. But, it's likely gonna be better than most Level 22 stock items you run into.