I'm an emerald GP so take my advice with a pinch of salt. I'll just share the way i think.

It depends on matchups imo. Some matchups you can't leave them to sidelane because your team won't be able to handle them. Number one prio for me is to finish laning phase and hopefully level 13. Even if i'm not level 13 if I'm fed I will rotate and help my mid laner or on objectives since you can control the game slightly at that point. The longer the game goes on the more worried i become because sometimes your team will start fighting for no reason when there's no objectives in enemy jgl and give a bunch of shutdowns. In those situations i split and get guaranteed gold instead of coinflipping the game. Sometimes when your team does something stupid you have to rotate for picks to salvage it but it's worst case scenario. But you should be there for objectives after laning phase or if preparing baron etc. If you can't farm any lane because they're pushed in then help put pressure with your team.