It depends on a few things. How big is it compared to how many chickens? If you go with the absolute minimum space, it is more likely you need to actively manage it, which means cleaning more often. What is your weather like? If you have wet weather you are more likely to have a problem than in dry weather. How close are your neighbors or your house? If the run is a bit isolated, smell is not such an immediate problem. But a wet smelly run is unhealthy.
To me, the key is smell. If it smells, it may need to be cleaned. If it gets wet for a while, it will probably smell some no matter what you do, so try to keep it dry. I have a large run and let mine free range most of the time, but sometimes I do keep them penned in the run, such as when I know I have a predator threat. As big as mine is and as seldom as I lock them in there, I still get a whiff when it sets in wet for a week or longer. Wet is your biggest enemy as far as smell and health go.