If you leave the cuttings they'll decompose and fertilize the soil, giving advantage to fast growing weeds. Possibly also add nitrogen deposition from surroundi

If you leave the cuttings they'll decompose and fertilize the soil, giving advantage to fast growing weeds. Possibly also add nitrogen deposition from surrounding industry/agriculture to that, and you have an ideal cycle for lots of biomass. Mowing like twice a year and removing cuttings on the other hand can and usually does break that cycle, can take some years, resulting in less fierce growth, and more slow-growing species.