If your jungler just ganked and killed the enemy support, and the adc is running around his tower and you're pushing it, get the damn adc, go back, get the tower, get dragon, gank mid, gratz, you just made 1500 gold
If you send your time chasing the adc with low hp you give the enemy mid and jungler an oppurtunity to come down to bot and counter gank you because you over extended(that is if you dove further than t1 turret), if you can get the adc to just B the chance that you get bot turret + drag is higher, you will have the time to do so because:
the support is dead,
the adc has to b,
the jungler isnt close to you(let's put this scenario where the jungler is top side:
You're jungler comes to gank, your support CC(assuming he has CC) the enemy adc/support and exhaust the adc, you get them really low and they flash into their tower. Right now the enemy team has noticed that you've ganked them and the mid and the jungler is moving bot(to help their bot out), if you keep chasing after you will lose so much time because it's not 100% that you will kill them because the further you dive the closer the enemy teams mid and jungler gets to you. Even worse, you'll take a couple of tower shots.
If you would just go back, take the bottom turret so that your minions would push onto the 2nd tier turret the enemy adc will have to go back, run back to lane, push the minon wave back THEN go to dragon. This way you would've gotten more than enought time to take dragon because the enemy team wouldn't be able to contest it if it was a 4v2.
tl;dr: Prests way: you gank bot, get them both low, chase them beyond 1st tier turret, give enemy team a chance to react, give them an oppurtunity to get to bot and contest dragon
My way: gank bot, get them both low, make them go b, take bot turret, take dragon, b.
