Off-meta is fine, as long as it's a good-faith attempt and you communicate it to everyone who it'll impact.
Me going Leona top affects basically just me, and at most my jungler as well since they need to pick someone with decent damage now if they want to gank. That's it, though, and people go damage junglers all the fucking time anyways, so that's not really something special I have to communicate.
When you start going to unusual strategies or picks botlane in particular, however, they need to be communicated. If you're going support Ashe I need to know that ahead of time and know, in general, what I have to cover for. If you're supporting some other lane than botlane that definitely has to be communicated, since it affects most, if not all, of the team, and I have to pick around that as an ADC. You don't have to warn me if you're playing Kalista as an ADC (although it would be appreciated so that we can actually use your ult), but if you're planning to take her midlane to stay there that suddenly becomes a concern I have to pick around.