The regex a?a?a?a?a?aaaaa against the string aaaaa will complete in linear time if you use non-greedy ?s but with greedy matching it has exponential complexity.

The regex a?a?a?a?a?aaaaa against the string aaaaa will complete in linear time if you use non-greedy ?s but with greedy matching it has exponential complexity. So, there is a difference.