This is a feature which got a fair bit of steam in some software, probably largely due to the fact that vB3 added it (largely as a gimmick, in my opinion). It's supposed to be a miniature control panel with features just for mods, however it ends up duplicating capabilities making software harder to maintain and it ends up bloating things. It does however restrict some capabilities like changing someone's group while still allowing a moderator to edit basic things about them. I personally think that something like that could be handled as an admin permission, however it could be considered a pro of the moderator control panel. A moderator control panel also means that a user won't need access to the main control panel which might be behind a demilitarised zone with countless layers of security, although I follow the model that if a software was generally more secure, then such a paranoid approach wouldn't be so necessary. Discourse for instance has a unified control panel, to my knowledge as does Gosora and some others.