As indicated in ACEC Technical Bulletin # 43, certain minor defects don't require repair, while other more significant ones do.
The decision to repair an SBS modified bitumen membrane, as with any other coverage roofing system, should be taken only after serious consideration, and must be based on the consequences to performance. Open joints, fishmouths at the overlaps, non-adhesion on large surfaces or surfaces where overheating has caused reinfocement distortion should be repaired as soon as possible.
On the other hand, unspecified anomalies such as minor wrinkles and blisters should be seen as inherent to the physical characteristics of these materials and their recommended methods of application. Patching a small wrinkle or blister for no reason other than to make look better isn't justified in the majority of cases and, in general, the repair will look worse than the original imperfection.