The sign-in code is sent as soon as you enter your email
Submitting your email address on the sign-in page sends the code straight away, and the code page names the address it went to.
Signing in with an email code is one step shorter. Enter your address and the code is already on its way, so the code page opens with the field ready for it rather than asking you to press "Send code to email" first.
The page also says where the code went. A mistyped address is now something you can see, instead of something you work out from mail that never arrives, and "Wrong email address? Change it" takes you back to correct it.