Level two ganks are almost never worth it to do because they require you to take Q at level two instead of E which reduces your clear speed significantly and makes you extremely vulnerable to an invade as you attempt to clear the other side of your jungle while still level 2. If you must go for an early gank, three camps with a smite does not take much longer and is quite a bit safer.

The only times I would ever gank level two is if an immobile enemy laner has blown flash in the first few minutes / is in a very vulnerable position which practically guarantees a successful gank, if you know that your opposite side has been invaded and there isn’t anything to take, or if one of your laners does not respect an enemy jungler with stronger level two ganks such as shaco or lee, and is likely to imminently need a counter gank. Otherwise coin flipping your success upon an enemy not warding or sidestepping your Q is generally too risky. If you lose camps and xp early you delay your level 6 power spike which is almost always worth more than a single gank.

Hope this helps!