Most homes whose drains run freely do not need drain cleaning on a fixed schedule. The “once a year” rule on plumber websites comes from companies that sell the cleaning, and those pages cite no code or standard. A schedule makes sense only when a line keeps clogging from tree roots, old pipe, or kitchen grease.
Tree roots are the main reason a sewer line ends up on a calendar. City sewer departments explain that roots follow moisture to cracks and loose joints in the pipe, grow inside, and are likely to block the line again after they are cut. Cleaning clears the pipe but leaves the opening. How fast roots return differs from one yard to the next, so a camera inspection of your line is a better guide than a date.
Grease is the other common cause. The North Central Texas Council of Governments warns that grease poured down the drain hardens and clogs sewer pipes, and says not to rinse it away with hot water. If a kitchen line keeps clogging from grease, changing what goes down the sink does more than booking cleanings. A line already coated with hardened grease may need hydro jetting once, then better habits.
The honest limit: a cleaning schedule does not repair a cracked, sagging, or root-filled pipe. If a drain clogs again within months of being cleared, the pipe itself is the problem, and more cleanings only buy time. A schedule does make sense for restaurant grease lines and shared stacks in apartment buildings.