Most automatic watches should be serviced every 3 to 5 years, though that's a guideline rather than a hard rule — how often really depends on how much you wear it, how it's stored, and whether it's showing any signs of running poorly. Skipping service entirely isn't a good idea, but you also don't need to rush a healthy watch in every year just because a shop tells you to.
Why automatics need service at all
An automatic movement runs on tiny mechanical parts — gears, springs, jewels — lubricated with oils that break down and thicken over time. As those oils degrade, parts wear against each other with less protection, which is how a watch that's overdue for service starts running poorly or, eventually, damages components that would've been fine with fresh lubrication. Service isn't cosmetic maintenance, it's preventing wear that gets more expensive to fix the longer it's ignored.
Affordable automatics with Seiko or Miyota movements are generally more forgiving of a slightly delayed service than high-end pieces, since the movements are simpler and parts are cheap and widely available. That's not an excuse to ignore service indefinitely, but it does mean the 3-5 year window has some real flexibility built in for everyday watches like the ones we sell.
Signs your watch is telling you it's due
A noticeable change in accuracy — running much faster or slower than it used to — is usually the first sign. So is a power reserve that seems to drain faster than it used to, or a rotor that sounds louder or grindier than normal when you shake the watch gently near your ear. Moisture under the crystal is an immediate stop-wearing-it signal, not a wait-and-see one, since it means the seals have failed and the movement is exposed. None of these symptoms mean the watch is ruined, but all of them mean it's time to get it looked at rather than waiting out the full interval.
If you're not seeing any of those signs and the watch is keeping reasonable time, it's fine to lean toward the longer end of the window rather than the shorter one. A well-built automatic that's running fine at year 4 doesn't need to be torn apart just because a calendar says so.