Reasons to bring to a shop, in the order of importance I (anyway) give to them:
1 - Make sure it's correctly adjusted, if it's not clear how to do so.
2 - Release check to ensure the boot lugs don't throw the system out of spec, if the boots are used or have had some work done that you're not entirely confident about.
3 - Release check to ensure used binding hasn't gone out of spec due to wear/dirt/whatever -- but, if this is your reason, you shouldn't do it when you get new boots or new bindings, but periodically (such as at the beginning of every season).
4 - Release check to ensure new binding didn't leave the manufacturer out of spec, if you're worried about that.
5 - Preserve cause of action against manufacturer, which you should really only have if the binding left the manufacturer out of spec, so this is just a repeat of 4.
6 - Create cause of action against shop in the unlikely event they misadjust the binding, though hoping to create an injury in order to sue for it is ordinarily not considered highly advisable.