Some improvement in performance after re-import av user in AX 2012 R3

Hi, 
 
We have a very slow development environment at a customer site we are planning to move to another server with some greater resources. but meanwhile we are trying to experiment a bit with this environment and we have found out that after deleing a user completely from Ax and reimporting the same user.. some of the operations we running much faster. Have someone came across such behavior? I actually wanted to share this experience to find out if it is normal and what could be causing slower performance as the profile gets older?