Clearing again versus finding out why
Clearing a drain is the immediate answer and it has real advantages: it is understood, it is comparatively quick, and it produces a working drain today. When a blockage is genuinely a one-off — something went down that should not have — clearing is the entire correct response and nothing more is needed.
The problem is that clearing is also the path of least resistance when the blockage is not a one-off. Each time it happens, clearing it again is the cheaper decision in isolation. Repeated, it becomes the more expensive one, because every clear treats the symptom of something that has not changed.
The signal to watch is the interval. If a drain blocked three years ago and again last week, that is not obviously a pattern. If it blocked eighteen months ago, then eight months ago, then last week, that is a trend, and the trend is telling you the restriction is getting worse rather than being resolved.
The second signal is location. If the blockage is at the same point each time, something at that point is causing it — roots through a joint, a displaced section, a low spot holding water. If it moves around, the cause is more likely to be what is going into the drain rather than the drain itself, and the cheaper fix is behavioural.
The honest framing of an inspection is that you are buying information, not a working drain. That feels worse than buying a working drain, which is exactly why it gets deferred. But information is what stops the cycle: it either identifies a defect that can be repaired, or it establishes that the pipe is sound and the cause is upstream of it. Both outcomes are worth having, and both end the guessing.