need not; (do) not have to — used after the negative stem to express lack of obligation or necessity.
明日早く行かなくてもいいよ。
You don't have to go early tomorrow.
その本は今読まなくてもいい。
You don't need to read that book right now.
体調が悪ければ、無理して出社しなくてもいい。
If you're unwell, you don't have to force yourself to come to work.
彼に謝らなくてもいいと思うよ。
I don't think you need to apologize to him.
need not have; need not exist — indicating that something was or is unnecessary or didn't need to exist/do.
そんな高いプレゼントはなくてもいいよ。
You don't need such an expensive present.
彼は来なくてもよかったのに、来てくれて驚いた。
He didn't have to come, but he came — I was surprised.
この機能はなくてもいいという意見が多い。
Many people think this feature isn't necessary.