Marking targets 1-49 I've always understood. Even if people ignore them, I think it's fine for a tank to mark on the chance that they do. Especially early on when aggro is hard to come by and AOE isn't really a thing.

Sleeping is also understandable before AOE is involved, but if you have 2x THM/BLM and a WAR tank, sleeping is very counterproductive.

Both, at 50, are unnecessary. Rarely will you run into something that needs to be marked, and rarer still something that needs to be slept. It's just not a thing at 50. You need to have aggro on EVERYTHING. As Cold_Raven pointed out, though, there are situations where you should mark, specifically if something in a pack needs to die asap. But yeah, it's a niche thing unlike early on in leveling.