I've booked a gas boiler service because my household insurers reminded me that if my boiler blows up, starts a fire or whatever, the insurance payout will be reduced if the boiler hasn't had a recent service.
On the basis that it's cheaper to have it serviced than fund household repairs etc I decided to go for the service.
Anyone who hasn't had their gas boiler serviced for a couple of years should consider it but I do know that for some of us it just can't be afforded.
If you rent, make sure your Gas Safety Certificate is up to date. Your landlord has a legal obligation to supply you with a fresh Certificate every year.