Most of newbies are directed (or suggested to edit) their sandbox, and most of the tutorials about how to edit Wikipedia suggest to use the Sandbox. With the new collapsed user menu, the link to the sandbox has disappeared from the first sight, and this may make the discovery more difficult for the newbie.
The collapsed user menu is good, but it should be a good idea to have the link to the sandbox by default outside the menu, and give the option to add it inside in the preferences (not viceversa, because the new users don't know they can change their preferences either).