Servicing - is it really needed every year?

Just wondered what your thoughts are - is it really neccesary to get your pride and joy serviced every year. When I first stared caravaning I purchased a second hand van from a dealer. he said it was best to get a service carried out each year to ensure the van was in good shape for the new season ahead. Taking his advice I had the services carried out. I ultimately changed up for a newer model  a few years later this one being just under a year old - the van had a pre delivery service before collection and this time the dealer suggested every two years was fine. It crossed my mind the first dealer was just trying to drum up business. I know we all want to be safe and I guess there is some common sense to be applied here.

PS I still get my van serviced annually regardless of useage