Cutting pony hair is one of the worst things you can do to a pony, imo xD. I'm in the definite no category. There are always other options, and time and effort can actually achieve a lot.
The only pony whose hair I've ever had to cut was as a child when my brush and grow got caught in my dance and prance. I cried a LOT over it, though Mum took it off so neatly you can't tell her tail is missing a small amount. That memory has lived with me a long time.
Please don't cut your pony's hair.