Although I agree with you, I don't think that's what OP was asking about based on this part:
I'm just thinking that if a hacker got access to one email they'd have all account information?
It seems they are asking if an separate email account for each service would be beneficial. My opinion is it would limit the attack if an email account was hacked, but definitely not worth the hassle. Email aliasing (like the comment above me says) gives you some of the benefits without needing to juggle multiple accounts.