There are a few, but I'll sumarize;

A) data merging. Merging multiple data sets together with auto-Inc is tricky - especially in the case of related tables.

B) data distribution /replication - especially on and off phones - especially if phones are creating data records offline, then syncing later.

C) parent-child forms. Parent has to be committed to the dB before children can be added.

D) data imports - again especially related data.

I'm not doing justice in such a brief question, each item above deserves a whole exploration.