Today I discovered the importance of a high IV when battling Pokemon. I got a Vapereon with IV 93% and another with IV 44%. Turned out after fully powering up each Pokemon, the difference in the CP between the two was about 200 points. This is significant.
Currently I’m only level 30, so I can only assume that the difference gap of CP would only grow between Pokemon with low IV and high IV ratings as you get your trainer level up.