I typically don't carry smoke grenades, I actually don't usually carry any grenades myself, and I typically don't use smoke grens even if I pick them up.
I use them to catch hackers.
Agreed, they work well to catch the wall hackers that are dumb enough to shoot through it, but you usually need more than just one instance to confirm hax. Can also help give away an aimbot as well so you know to go to spec if they're tearing people up through smoke.
I don't see much good use for them in TDM or TS personally. Could be part of some strat, but most of the time just get annoying IMO. Can function as a distraction though.
In Bomb it can be useful to smoke the bomb area when defusing or if you are wearing tacs while defending but it really has to be part of your team strat to work out.
In CTF they are used to smoke the opposing teams flag area. This makes it more difficult for them to shoot you as you take the flag, but can make it more difficult to grab and run with if you aren't extremely familiar with the map.
And when bots are on the server, don't use smoke. There is nothing I hate more than people throwing smoke just so the bots can pick you off through it; they're annoying enough with their full body armor and AKs, don't need to give them another advantage