What I mean by this is that sometimes I will see the top laner just follow the jungler around and do a full jungle clear. I understand why they would take a single camp for the level advantage, but I don't understand why they would just help the jungler take all their camps.
Wouldn't that set them behind? I only ever see this happen in LCS.
Jungler gets their first buy much more quickly?
I'm by no means an expert, but generally this is only seen when a lane swap is instituted, meaning your top laner would have to sit in a 1 v 2 (versus their ADC and support, assuming the support doesn't roam). Because of the 1 v 2, the top laner can normally get bullied away from lane, losing both CS and experience, making it hard for them to have an impact in the game. Even if he doesn't get forced out of lane, the top laner is susceptible to turret dives from the other team (because he'll be behind in levels; also assuming the other team sends 1 or 2 other people up for the dive). The double jungle strategy is simply a way to try to avoid all of that. By allowing the top laner to share some jungle experience on the first clear, he can pick up a few levels before he ever goes to lane (against the 1 v 2, remember), which makes his life a heck of a lot easier. It'll be much harder to zone him away from CS and exp, and he'll be a lot beefier, making tower dives harder.
TL;DR: Double jungling gives the top laner exp and levels so he fares better in a 1 v 2, lane swap scenario.
