The "annual service" is primarily a cleaning of the air channels that cool the PEM and motor. It's more important for the 2.x cars than the 1.5, as the 2.x design tends to pick up more debris from the roadway, packing it into the PEM and motor cooling fins. My 2.0 car, used for a 50 mile/day round trip commute, needed to have this done about yearly, but I've read that some 1.5's can go longer with little accumulated junk. It's a matter of what kind of car you have, and where you drive. I don't think any car would need to have this done 2x per year, unless you regularly drive on very dusty dirt roads.
One thing to be very careful of is that there are some connectors between the PEM and the car that are marginal or under-sized for the load they are carrying. This is especially true of the one that drives the cooling fans. Repeated disconnects of this connector can wear the contacts, leading to a failure. Replacing the PEM-side connector can be difficult (the standard procedure is a whole PEM swap), so I would do this service only when needed, so to not cause more contact wear than necessary.
Finally, it's a good idea to regularly (monthly is good) pull the car's logs onto a USB stick. Save them for recording long-term trends (e.g. battery health), and check for any error codes that might get logged indicating something going bad. (Search this forum for instructions on downloading the logs, and for where to find viewers.) Not everything gets reported to the driver via VDS display alerts. My car's challenges with that fan connector, and with one of the motor sensors were found and diagnosed via the logs.
Don't forget to check the normal stuff - your tires, brakes, washer fluid, etc.