In my opinion, the recommended servicing of every 3 or 4 years is just an easy way for the company / watchmaker to make your money.
If the watch still runs well, why spend the money to service? Also, when you send in for service, there is a risk that your watch may come back damaged. You know never know, some apprentice watchmaker may be the one "servicing" your watch. Look around forums and you will find it's not uncommon to have watches come back from service with scratches / nicks / dust, etc.
If the watch is still in production, and it's not difficult to find the parts for it, my view is just to run it until it no longer runs well. When you finally send it in for service, they are going to replace all the worn out parts anyway, so why bother sending it in early?