When I say "time to get it serviced" I am simply going on time frame as everything is working fine though it has been sitting unused for two or three months. Though I know it was serviced just before I bought it, I will likely have it all serviced this year just for peace of mind. In this case I am really just looking to what is common practice in terms of service regularity. As for computer, do they actually service anything or just change the battery and if so why do I need to take it every year if its working ok.
If it was professionally serviced before you bought it, was not heavily used since, and it was working fine three months ago.... not time for a service yet. If everything appears to be functioning fine, you are good to go.
If you are concerned about it, have your LDS check it out for you (there should only be a minimal fee).... it should take all of 3 minutes to check the regs and BC.
Now, here is a more complete answer:
As far as service intervals, you'll find two very different "camps" here on scubaboard:
1. Get it serviced annually, no matter what, because you need to in order to keep your warranty in place, and
because it is life support!
Many (most?) divers fall into this group; this is what the manufacturer recommends and the dive shop pushes... there is nothing terribly wrong with this, but read on...
2. Inspect & test frequently, but service
only when needed based on results of inspection / testing.
Group 2 tends to include the folks who've learned how to repair their own gear, regulator techs, etc. (In case you have not guessed, I'm a Group 2 guy

)
There is nothing
wrong with doing the annual service thing (assuming a competent tech), but the reality is that the Group 2 folks will actually have LESS failures than the Group 1 gang, because they are proactively inspecting and testing their equipment more often than once a year, and will probably find any problem early, before it becomes a REAL problem.
Best wishes.