Manage Issues and change requests:
Many times after delivering the modules to the 
clients/stakeholders, the clients may also feel to change 
some parts of the project. They may raise the change 
request or new enhancements for that particular module. 
During that time, the project manager needs to provide the 
updated estimation for those change request or new 
enhancements. They also make sure the change request or new 
enhancements should not produce any defects or risks and 
affect any other 

reference:
http://www.sphur.com/?p=71