User blog comment:TheNewBuildGuy/Possibilities-- Jungle Zyra/@comment-5324850-20130227020406

the exp you take from the top laner will cripple your top laner when you leave

when you go top and stay there for several levels you give time for your enemy to counterjungle all your camps

the enemy can gank freely knowing you wont countergank at early levels because you stay at top

zhonyas and rylais are too high cost for a jungler, especially one that gets no farm early levels because they are supporting top