Help me understand - Hairdressers using clippers

[penguinparty00]

I'm at the hairdressers and the owner who is lovely but expensive because he is highly trained in London uses clippers on womenswear hair to cut across, I am so untechnical so I wondered can someone explain to me the reason behind the clippers and why it's so expensive ?

I don’t like it, my hairdresser did it in my DD’s once and it was a dogs dinner when we washed and dried it ourselves. I think it’s supposed to be more precise but seems a bit like a fad to me.