depends on the mileage of your car and what car you have. In your owners handbook/service record, it has a checklist of what should be checked/changed and how regular.
They check/change all belts, all brake parts, fuel filter, all pipes, spark plugs, oil, oil filter, seatbelts, air filter (unless you have a big aftermarket thing), any visible signs of leakage, chafing of joints and gaskets, steering gear, suspension components and i'm sure i've missed a few bits out. It depends on what level of servicing you go for. If I ever take mine. I say check evertything, but be aware, I do know what i'm on about so I will know if you are fleecing me.