Pros~
*Good if you are not doing so well top.
*Tanky- Is very hard to kill late game.
*Cleans up team fights fairly easy.
*Very high Damage output.
*Ganks usually end with a success (after level 6)
*Very strong against champs with little amour/health and CC

Cons~
*Prone to be ganked early game.
*not too strong against mobile, ranged champs with amour pen.
*Not a good idea to charge in 1v5 if your not certain you will kill them.

Ganks by your team top lane usually work well with olaf. He is able to slow them enough for the whole team to catch up (if you dont miss your q and pick it up straight away).