User State Migration Tool (USMT) is a scriptable tool that is used to transfer the user data so you can upgrade an OS or provide them with a new computer. It is designed to retain most of there user experience from the previous computer and to make sure that their data is where it is supposed to be. The question that came up is, what does the /UEL option do?
The /uel switch replaces the /user option from previous version of USMT. It allows you to migrate only users that have logged into the source computer within a specific amount of time. This prevents you from transferring data from users who may have logged into that machine for some reason in the distant path, but most likely do not need their profiles moved.
The syntax for this option in the SCANSTATE command is [/uel:NumberOfDays|YYYY/MM/DD|0]
/uel:0 will migrate all data for any user who is currently logged on.
/uel:90 will migrate data for all users who have logged on in the last 90 days.
/uel:2002/1/15 migrates user data for all users who have logged into this computer since January 15, 2002.