You can't just turn up at an airfield and land, you need to talk to the controllers and get permission in case someone else is already using the runway. In order to allow controllers to keep track of which aircraft are landing and when, aircraft fly a "traffic pattern" round the airfield. This is a standard flight pattern at a standard height so that everyone knows where you are, and you know where to look for conflicting aircraft.
A standard airfield traffic pattern
The traffic pattern also acts as a little ritual for pilots. The pre-landing checks are carried out during the downwind leg (brakes off, undercarriage down, fuel pump on, etc.) and the standard pattern means that pilots run through the checks every single time without needing to think about it.