Different oil patterns cause the ball to react differently.
Parts of the lane where there is more oil, the ball will hook or catch less. Parts of the lane with less oil will cause the ball to hook more. The different patterns involve different concentrations of oil on different parts of the lane.
Strategies must change due to the way that the ball reacts. A bowler who relies a lot on his hook must change his strategy when the outsides of the lane have lots of oil, because his ball will not hook that much.
Typical bowling alleys have very consistent oil patterns, where the oil is a uniform rectangle for most of the lane's length. However at PBA events, the oil patterns get much more intricate, such as the cheetah or scorpion, to make it more challenge for the pros.