dovecot-lda "-f" argment optional?

[Sebastian Arcus]

I use dovecot-lda to deliver incoming email from Exim to Dovecot.

After having some problems with email bounces with empty envelope sender 
not being delivered because of an empty -f argument, I discovered that 
Exim can pass email to Dovecot using dovecot-lda without using the -f 
argument at all. Would this have any adverse effects anywhere else? The 
docs don't even seem to specify if -f is optional or not - but I guess 
it is - as it seems to be working without it. Does anybody know what is 
its role? I'd like to understand things a bit before I just start 
removing it permanently from my setup.