Should a button communicate the current state, the intended behavior, or both?

When I magnify a window in Chrome, I see an icon like this:

When I reduce the size of a window below it's normal 100% I get this:

Clicking either of those icons gives me options for modifying the magnification level.

On DEV when I am following someone I see this button. Clicking it makes me "unfollow" them.

We're inconsistent in our UI in that we treat the home page "save" button differently by offering a hover state which indicates the intended action.

As we seek to make this behavior consistent, I'm curious what you consider to be fundamentally correct behavior. This situation is handled differently across the web but I'm curious if anyone feels like there is a true best practice.

All comments on the subject are super appreciated!