Yes I would say it's worth it. First of all it means that your luggage isn't being stored in your car for the whole day (imagine if the car was stolen.)
Secondly, you check in early which means you have a better chance at getting the seats you want on the plane and being sat together if you haven't pre booked your seats. If you left it and checked in in the evening after dropping the car off, all the people who did the free time check in will have had priority over you as it's first come first served.
Finally, it means that when you arrive at the airport you can bypass that queue and go straight to security and into the departure lounge, a blessing at the end of your last day when you've probably been cramming in as much as possible (and are quite emotional at the thought of going home if you're anything like me!)