Depends on if you are going against someone who is loose-passive or loose-aggressive. A tight player generally won't 3bet light against a loose aggressive player. By definition a light 3bet is a 3bet with holdings that are behind your opponents pf raising range. So doing this against a loose-aggressive player is asking for trouble. Doing this against a loose-passive player however is a good way to get a fold pre-flop and widen your 3betting rate.
3 betting light is definitely profitable but as the poker pros say: it's all about looking for the right spots. It's most profitable with strong drawing
hands (KJsuited) or pocket pairs, and obviously more profitable in position. From OOP, I would consider it a "3-bet
bluff" more than anything. Which is essentially the same except for the mentality going into the hand.
If I'm OOP and there's a few limps and a late position player raises and I look down at pocket fours in the blind I have to consider my options. I can fold (nothing wrong with that). I can call (bad idea as there will assuredly be callers behind and pocket fours is a losing hand multi-way). Or I can raise (insure I'm against less opponents and have fold
equity). Generally speaking I want to mix it up and switch between folding and 3betting. But the ultimate goal is this: if I'm going to make light 3bets it's so that I can get my strong 3bets called. If I never 3bet without AA or KK I'm not going to get a lot of action on those holdings. So 3betting hands like 44 or KJs are ultimately to raise my 3bet rate so my AA/KK hands get called.
3betting your button... well.. people will disagree with me on this but I prefer to flat my speculative hands. I have position and people don't respect button raises quite as much. If I'm not getting respect on my raise I should be raising with stronger hands, not lighter ones.