Or unless your lanes were already loosing by enough that jungler interference foes nothing. If i find myself in a situation where 0/6/0 Wu keeps jumping on 6/0/0 Darius and die, i don't even bother coming there and dying with him. If he is stupid enough to feed enemy (not dying under your own tower due to tower dives from mid+jungler+top players, but just pushing lane, dueling with fed enemy and losing), you won't succeed in ganking.
However, i haven't played jungler in a while, and last time i've played this role i was Heca, so, farming for extra time didn't hurt.
There is a lot of things that jungler have to keep in mind and have to get help with to make a successful gank, like, deward, creep equilibrium, CC dispense, mind games. Off course jungler can gank without it, but it really helps, and if there is a 50/50 chance that gank will fail, i don't bother, i'll probably take enemy wraiths and will wait for a better opportunity to gank.
I don't get what the hell with people tho, when this mentality of miraculous ganks from jungler will stop, every single time someone loses lane, he blames jungler for not helping him, when there was no freaking possibility for a gank. Calling a jungler is not like calling for GP ult, it won't happen right now if you chat "omfg gank noob panth already ganked my X times" or something like this