The issue I have is not remembering them, as the password manager does that. The issue is more when companies rely on your email address being the same for different parts of the service or they take my PayPal email address and use that as my email address.
One of the most annoying is when contacting customer support by email and they reject andy@ at and now I have to find a way to send an email to them from ocado@ or whatever email address I chose.