Currently, power actions (i.e. restart, shut down) and user actions (i.e. log out, switch user) are found under the same “power” button.
You see, having power actions here makes sense, but user actions are a little unintuitive. I often have to squint my eyes to read the text-only label and then point at the item (which has a narrow height). When you’re in a rush, it’s easy to misclick.
elementary does this separation between user and power actions. The user button is filled with the user profile picture (or the initials).
By adding a separate button containing only user actions, we also gain the opportunity to display the profile picture more… 
