It depends. You have to send someone with waveclear because if the wave crashes on the tower and you just sit mid as 5, you lose that tower for free. If your top or mid has teleport, preferably send them to clear the wave so that if the enemy team tries to engage, they can teleport in to the fight. If not, send the person that can clear wave the fastest so they aren't gone as long.
It's preferable to not let the side lanes slow push into you in the first place, but if they start building up huge waves, it's up to your discretion to make the best call in that situation, but doing nothing about it is the worst call.
this is true but I play a lot of soraka, janna, karma and sona and I don't have enough damage to wittle the super creeps down, sona might be a bit different but I don't build lichbane on her much anymore, stopped doing that when I got better at using my actives. to address another thing most top laners I get don't bother taking tp because it "falls off", I shoulda mentioned that but still. :(
basically we'll have some somewhat-fed diver like a Vi or a Yi that keeps wanting to charge in 3v1, you know those people. though that's more early-midgame, not so much late but it continues until late, where some think kda will win a game. so I just stick to them like glue, get my wards up and if they go in, I usually have a redemption, locket, other tools to keep them alive so fights actually go in our favor, then make a call off of that. it's sloppy but constant fights are typically where I can keep those types alive. assuming, y'know, they weren't feeding but it's worth a shot if my adc can play safe for a bit
ok I went on a whole speel about that and the tl;dr was I'm typically around silver in my norms, most people don't know how to close out a game or stall a game, powerspikes, etc. follows the rules of usually whoever engages first wins, assuming they've got backup since both teams are at a standstill every single game. Or that's what it feels like honestly.
I can usually get the map into a pretty favorable position for my team when I'm playing support if I've got a friend or two, not the best shotcaller but doing something is better than nothing. tends to work out most of the time. this is why I pretty much only play tanks top with TP, not great at using ignite on others. unfortunately not many people ward(or ward at all) for me to flank to. I forget, is it possible to TP onto a blue ward?
edit: yeah normally as the adc(assuming I have a no-tp top or mid, or waveclear mid for that matter because assassins amiright), I go clear the wave real quick while my team engages, or was playing too far forward and the enemy team got bored. happens from time to time