Collecting materials for endgame gear.

[Tonuss]

Remember that time spent is also "money," especially when you can spend that time on dailies instead. The only time I would spend is figuring out if it's more cost effective to buy the robes or the mats.

Edit to add: I've been auctioning a lot of my tradeskill mats for some time now, with the exception of whatever I need for leveling my skills and a few items left aside as a "just in case" kind of thing. Since the cost of materials will go down over time, selling off my mats now and buying them (or the finished items) later gets me a net profit overall.