Fastmail talks about the value of masking your email address on its website. “You wouldn’t give your name and home address to just anyone. Companies can sell or leak your email address. Using a unique email address as a substitute for your real email adds privacy when you sign up for online services and shops.”
As far as checking your email goes, Fastmail will take all of the mail you receive from the masked email addresses and put them in one inbox for you. This way, all the garbage, and spam you get from services you sign up for will be available in one place. Plus, you might get some mail you want to read, so having one inbox to check them is nice.
Important to note is that the aliases don’t expire unless you manually delete them, so you’ll be able to keep your apps and services active with a masked email address for as long as you want.
1Password is making a case to become the go-to password manager. It keeps getting new features, and its partnership with Fastmail is just another one that makes it even more worth a look.