Way back when I started playing WoW I had somehow decided that auto loot was bad. Maybe it was the limited bag space or perhaps it was the previous game I played required clicking and dragging each piece of loot individually to my bags (including coins). Whatever my reasoning I never really looked back.
Then quite a few months ago I discovered/rediscovered the auto loot modifier key and start using that pretty much ever single time I looted. For some reason I still didn't enable auto loot at that point. The most annoying shortcoming of this method was that when I was mining, skinning, herbing, etc, and hit the auto loot modifier mid "cast" that it wouldn't apply unless I had it pressed at the start of the cast. I suppose that is an auto loot modifier bug.
So a couple weeks ago I took the plunge and decided that holding a modifier key every time I loot and/or gather was stupid; I enabled auto loot on all my toons (apparently it isn't a global setting). It took a couple days to get used to not hitting the shift key with auto loot on since the modifier I had used for so long to auto loot now had the opposite effect. I can't believe I didn't just auto loot from the beginning.
I think the one add-on that made auto looting a possibility for me was one that could throw away my cheapest vendor item as well as show vendor items by their value in ascending order. Before that I had to look through all my bags (which always seem to be full) and see if what I was picking up was better or worse than what I had. I don't really make the effort to visit a vendor to sell stuff until I have to start chucking those grey items worth a gold or more.
People might think the hybrid tax is measured in performance vs pure classes, but it's really paid in bag space. My druid carries around 4 sets of gear (DPS, tanking, healing and PVP) plus various potions, scrolls, food and whatnot. I think I have 7 bag slots free right now with four 22 slot bags. I really need to burn through some consumables rather than try and ration them. Meanwhile my pure DPS toons are walking around with 47+ free slots.