We see that setting
- Nicely leaves only 'Log in' in the upper right corner of the screen.
- Nicely leaves only the 'Log in' box in the middle of the screen.
However, the <title> and <h1> still mention both "Log in / create account"!
The use might wonder "hey, where can I create the account it mentions?"
(Indeed, you might even go the whole hog and make Special:SpecialPages list it differently too.)