I did 'no mow May' this year and my neighbors hated it. The dumbest part was that the grass wasn't any longer than the flowers I planted at the same time.
My next door neighbor cuts his grass so short you can see all the 'bald' spots of dirt because he won't let the grass grow enough to cover it. He's very proud of it.
I never get it either! I have a part of my garden as lawn because it makes a nice place to sit in. But I never mow shorter than ~10cm. The lawns that are mowed so super short always look unhealthy to me...
I never understood why grass HAVE to be short. Looks unnatural and plain. Plus the effort in maintaining it just annoys me. Sure, it looks clean, but it looks devoid of life.