LTE: In what scenarios a MME starts using new Kasme ?

Question

I know during the attach procedure, MME may get one authentication vector or more than one authentication vector.
Now question arises, what is the use of keeping multiple authentication vectors at MME ?

Answer 1

When MME receives messages like (attach request, tracking area update) without valid KSIasme and MME already has an EPS security context , MME re-authenticate to UE and generates/uses a new Kasme.

There could be another possible reasons but I know only one reason for now.