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ca be goo, if the jungler know wha he ez doing.

It is goo

yes it's personal preference

I wouldn't say having a full on jungler is necessarily good, but making it a priority to clear out jungle camps whenever you can (like when your lane is pushed) is a good idea.
Extra XP and gold is always nice and lets you get ahead.
Also whenever someone's missing from a lane it puts pressure on the opponents because you could be coming for a gank, even though you're just clearing out the jungle.

I sometimes play Cho with smite, laning at bot until lvl 3/4 then from that point mostly just clearing out camps and ganking, and covering lanes when someone's dead/recalled.

I do the same thing with Nidalee, Once level 6, I lane in human form when the lane is not pushed, and flip to cat form to clear the jungle camps real quick for easy cash. Best part is, if they push back I can easily get behind them... Being Nidalee and all...

I main jungle, and absolutely,

The thing is with jungling, you give up a lot of lane presence as opposed to running a 2v1 but at the same time, a jungler will out-level (substantially) any non-CSing champion in a duo lane. If played correctly you end up with a lot more map-control as well as higher team-wide level, and higher team-wide gold.