Most Helpful Guy
You should have the ability to use everything in the right way if and when require.. See what suits you and go with that. Everyone will not like it the same way.
Most Helpful Girl
You don't have to use them if you don't want to but they do serve a purpose. Primer helps prepare your skin for makeup. It helps makeup blend better, wear longer, can prevent creasing, etc. Powder helps "set" makeup so it will stay put during the day. Some people use it to help minimize shine too.