Rooting is just gaining root access to the system, in other words SuperUser permissions. It changes nothing else other than allowing anything to use superuser permissions. SuperUser.apk (the application) is used to prevent anything (other than the system itself) from using superuser permissions unless you allow them. Without the app, anything and everything could run with superuser permissions.
It does not grant access to free programs, it also does not allow for system backups (nandroids) though it is a step towards that goal (backups). For backups (nandroids) you need a recovery, root doesn't provide that, though it does make it possible once a recovery/bootstrap is compiled for the Droid 3.
It does allow you to use root applications though (Wireless tether for root users, Titanium Backup for root users, etc..) that provide more functionality than the stock OS allows.
Titanium Backup is enough reason in my opinion for root. If you ever need to "Factory Reset" your phone...or it's damaged and you replace it........titanium backup allows you to have made a backup of not only your apps, but the settings/configuration of those apps (game levels, license codes entered, etc...) so you can easily restore the data back along with the app. Definitely a plus..
Root can later bring about recoverys (for entire system backups and installing custom roms) and custom roms....