It means somthing like "why should I stop partying/having fun?"

It's from the song featuring Lil Jon, and it basically means "I'm drunk/high now and want to get even more drunk/high. I don't want to sober up". It's just a funny way of saying "let's keep drinking"

Well, Turn Down for What was actually a song a year ago (?) and it was really popular. You can actually find it on Youtube. It doesn't have much of a meaning but it means to keep having fun/Why stop having fun. It's really meant to just keep having fun, although I haven't heard it anymore (I'm a teenager, so we used this way more). I think you'll find them more on old memes though~ I'm sorry if I didn't explain well. There really isn't a meaning to it.

Turn up means get high, (smoke weed, do drugs, party, alcohol, etc.) i've always thought turn down meant to sober up. So turn down for what means like "why would I sober up for that? im gonna stay high"