dovecot-lda "-f" argment optional?

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.