[Fuzz]

There is a persistent rumour going around that cutting your lawn extremely short before the winter is beneficial, or even necessary to avoid growing mould under the snow. (I also think that many people think somehow that cutting extra short will somehow turn your lawn mower into a leaf-sucking vacuum cleaner??) This seems to arise from a misunderstanding about the plant health problems lawn debris can cause if left over the winter. Some people seem to think that leaving ‘long’ grass leaf blades on your lawn will invite the same mould problems a carpet of tree leaves would.
But the lawn mowing mantra we repeat all summer – two and a half to three inches for best grass health – is true even in the fall. There is never a valid time to mow down bluegrass, ryegrass or fescues shorter than their ideal healthy height.

more:

https://lawnsavers.com/blog/fall-lawn-mowing-myths/