User blog comment:StrategicMagic/Jungling for the Terrified and Below lvl 20/@comment-81.200.170.248-20120815214243

Clearing speed is major. The faster you clear the jungle the faster you get levels which lets you do a good gank off sooner. Those 20 seconds you talk about is the differnce between the opponent getting lvl 3 (top) and 4 (mid) before you show up or not. It's can also mean the enemy ganks the lane first and your teammate being dead before you can get there.

Second you don't want to start dorians shield, or cloth armor, or regrowth pendant. Mid and top always start with boots (and the AD carry bot lane probably does too), so unless you do the same you'll be slower than them and your ganks are alot less likely to succeed. And boots also give the best clear speed since less time is wasted moving between camps...