The idea behind the service center is to expand the gas station with a small service/garage building.
Since the gas station is basically in the middle of nowhere, customers who run into trouble with their car on their journey will find your gas station to be the only place for urgent repairs in the area. We are talking smaller fixes here, like a small garage would do in real life.
Another aspect of this addition to your gas station is the ability ot expand it by a towing service. While you won’t drive yourself and tow cars that broke down on the road, you’ll be able to hire someone to run this part of your business for you. It will generate additional revenue on its own, but also provide even more customers for repairs.
The service center will require you to keep an inventory of common spare parts in order to be able to make the repairs. This means that if you decide to go that route, you not only have to invest into the building and its equipment, but also keep a significant investment to maintain the spare parts inventory. The profits that the service center is able to generate can be substantial and allow you to finanse further expansion.
https://store.steampowered.com/app/1149620/Gas_Station_Simulator/