okay, that's good to know...
I only raised this as I was on a customer site during an upgrade and we had issues with PFUD/logging on.
Quite a large number of users had a "all users role assigned", however, due to dual development stream the the new version of the role had a different profile Id. Therefore, when PFUD ran it had to do a heap of read/writes/inserts/deletes to remove the old profile from the user and add the new one. PFUD placed a enqueue lock on the user and did not release the lock until after the COMMIT (makes sense). However, it means all users were "locked" until that one role was finished.
Whilst this happened, users would attempt to logon but could not. We had suspected it was due to the enqueu lock and need user login sequence updating USR02 (unless it was refreshing USRBF* buffer tables).
As a result, I assumed the login sequence to SAP had a lock statement for the user tables.
Regards
Colleen