[fetchmail]Fetchmail Multidrop Mail Loops

I am planning to set up an multidrop account which will fetch mails
 for allusers in my domain.

 I was going through the Multidrop section in the Fetchmail manual.
 It mentions this also....
 'Be careful of  mail loops if you do this!'

 Can anyone explain and help me out with what this really means ??

rgds,
waly