Need (something) Like (one Needs) A Hole In The Head Idiom
This
database is a comprehensive collection of all the American idioms and slang available.
American Idioms are many and varied. We hope you enjoy our collection. We are adding more all the time.
.
to allow the details of a situation to obscure the situation as a whole
The man is not able to see the forest for the trees and always allows his obsession with small details to obscure the larger picture of what he is trying to do.
Hereby is used sometimes in formal, official declarations and statements to give greater force to the speaker' or the writer's affirmation. People will say it sometimes to emphasise their sincerity and correctness.