A fixed-speed compressor cycles on and off. If it runs 40 minutes in every hour, its duty cycle is about two-thirds. Duty cycle rises with ambient temperature, door openings, warm product, dirty condensers and worn gaskets. It falls at night, in winter and when the cabinet is left closed.
Designers size systems so that the compressor still has idle time in the hottest expected conditions. That reserve allows recovery after deliveries and room for defrost. A compressor running almost continuously in normal use has no reserve, so temperatures will drift on busy days and the compressor itself runs hotter and wears faster.
Watching run time is a useful early warning. If a cabinet that used to cycle comfortably starts running nearly non-stop, check the obvious first: condenser cleanliness, airflow around the unit, door seals, overloading and the setpoint. Inverter compressors behave differently, running longer at lower speed, so compare their speed and power rather than on-off cycles.