What it should do (i think) is issue or not issue the "ifconfig-pool net/mask" option in the config file (if you follow the logic). But, I found the following, from my observations:
if you try to use "ifconfig-pool" in the advanced options, you get an error (in the logs) saying that you cannot use ifconfig-pool and "server" at the same time, because "server" already creates a pool for you. Indeed there's a "server" option in the config.
the server option is not very flexible because it is kind of a ifconfig + ifconfig-pool in the same option, and the server takes the 1st address and all the rest of the entire range is reserved for the pool. I like to issue a ifconfig-pool where I use only a portion of the range, leaving another portion to static IPs in the client overrides.
from googling, it seems that in the old days there was a configuration text filed where you would indicate the range for dinamic assignation (just what I expected) and that would issue a separate ifconfig-pool config option (or not). I was then changed to, when on (presumably) issue a server command taking all the range and (presumably) when off, switching that command back to a normal/simple ifconfig (which I would be happy with because it would allow me to issue a ifconfig-pool in the advanced options).
In the current state it seems useless. But maybe I'm missing something.