[Dovecot] Actually what is the SQL DB used for?

Is a RDBMS required for Dovecot to run in small (SOHO) environments? (Does it store indexes to the mail, etc.?) Or is it strictly leveraged for larger-scale environments?

I'm asking, because the INSTALL says ./configure and make is enough for most...but as my previous post requested...there isn't anywhere that lists Required Packages/Software. We need to get that out there before 1.0RC becomes 1.0! :)

-AJ