My thoughts are:
Grass is cut
if you want to cut hay for your livestock, or need the cut grass for some other purpose (such as roofing material, mulch)
if you want to avoid seeding and producing hard stemmed grass, if you want good quality hay for you livestock
if you want to reinvigorate the grass – producing tender grass, more shoots, encourage more roots
if you want to control some kind of potential pest (depends what you consider pest)
if you want to avoid spread of uncontrolled fire
if you want to have a nice looking grassland
Grass is not cut
if you have no projected purpose
if you want to retain a landscape that protects you from various elements (rain, wind, neighbors?, etc.)
if you want to let nature take its course
if you want to retain an all natural untouched area, a sanctuary for different kinds of life
I hope I am right, and these help