AFS access permissions and OSX interaction

[nepywoda@fnal.gov]

Earlier I posted to the list about changing the local UID to match the AFS UID in Mac 
OSX. Some people suggest doing this, but I've never come across the true reason behind 
it. What I'm wondering is, if 2 people have the same local UID, say 501, different AFS 
UIDs, and login at the same time...can person 1 fool AFS into thinking it owns person 2's 
files? This seems like a huge security issue to me, so I doubt that would be the case.

Does anyone have any definite info about why we should change the local uid and the 
local file uids to match the AFS uid?

thanks,
~~~Paul Nepywoda