That's an entirely personal decision. It's definitely not a necessity, its purple optional. There's nothing harmful about using Hide My Mail if you want to. I'ts a feature that lets you at any time stop receiving any email from any website you may have signed up on.
Wether it's a known, trusted website or newly discovered and possibly shady one is not relevant for using it or not.
It does of course make sense to use it with websites you don't really know, but by that same token, it would make sense to use payment methods that you can easily cancel or block in those same websites.
At the end of the day, its up to you. Its helpful if you ever decide you want to stop getting any email form those sites and don't want to go through the hassle of going to the particular website and cancelling your account. You merely delete the fake email address that was used with the website.