Please tell me I have not been doing this wrong...

Everytime I flash a new rom I hit wipe data/factory reset and do it twice. Thats it.

But i just saw somewhere to go into mounts and storage and format /system.

Is that needed? Because I have never done it. Does the factory reset selection format system? because I have never had major problems, and I just wanna make sure I am doing it right.

Thanks.