Note: This isn't a question about two-factor authentication where the user needs to type in a token in addition to its password.
Browsing through a series of major websites such as Google and Apple, I noticed they were changing their login forms to handle authentication in two steps: First asking for the user's email on one page and then requiring its password on another page.
It seems they're initially checking to see if the submitted email is associated with an existing account but I always thought that was bad practice because it made it easier for hackers to compromise accounts.
In the middle of a redesign on one of my websites, I'm wondering what benefits such a system brings, if any?