It is a good idea to have your generator serviced at least once a year. Oil that sits still has chemical action occuring. Starter batteries (if so equipped) will be weak or simply fail if they sit for long periods of time. Fuel systems can clog up and prevent starting just when you need the generator. Or the clogged system may run erratically which is hard on the generator engine and very hard on your appliances if the generator power is going up and down.