[Closed] Rear Shock Servicing

I have a 5th Element (air) rear shock on my Superlight. It is maybe 3 years old and is still performing well, no signs of deteriorating performance etc. but I am conscious that it will need servicing at some time. I only ride the bike in the summer (the rest of the year is usually rigid ss or a HT) so if servicing is a good idea, now is the time to do it.

I suppose the question is - would a TFT service make much difference? How long should you leave it before servicing? What signs that a service is due should I look for?