Are there any examples of the utility of doveadm stats?

in the man page:

dump accepts following types: command, session, user, domain, ip and global.

   Filter can be

   user=<wildcard>
          Match given user.

I've tried the following commands after looking at the (sparse and example-less) man page.

# doveadm stats dump metric_name field count sum min max avg median stddev %95 # doveadm stats dump user Error: Extraneous arguments found: user # doveadm stats dump user user="*" Error: Extraneous arguments found: user user=* # doveadm stats dump global
Error: Extraneous arguments found: global # doveadm stats dump global user="*" Error: Extraneous arguments found: global user=* #

I assume there is more to the configuration for stats than merely making it not report an error. So, the first question is what sorts of stats would be most likely to be useful and what do I do in the configuration to get those?

Second question is why is this required to be enabled if, by default, it has no functionality?

-- Beware of geeks bearing .GIF's