I tape my mouth because I hated waking up with a dry mouth that tasted horrible. I've also read that this contributes to tooth decay.

It's just a small piece of tape, as big as half a fingernail. It's placed on my lips right in the middle, and it works more by reminding my brain to keep my mouth closed and less by actually mechanically holding my mouth shut. If my nose is stuffed, I can just open a slight gap between my lips to breathe through. Otherwise, though, when my mouth is that close I will automatically close my lips and breathe through my nose through the night, which anecdotally improves my sleep quality and reduces morning breath.