I know a round brush gives it more volume, but what makes it straighter and easier? What is your personal experience?

if you are going for volume use a round brush my salon i go to uses a round brush to straighten my hair (my hair is really curly and i can't straighten with a straightener so i know that a round brush works alot) i was reading a magazine the other day and it said for flatter straighter hair use a paddle brush