This functionality is currently available only on Onshape's browser platform.

Assembly toolbar with Named Positions feature icon highlighted

Assign a name to a specific position (that is, the Mate degree of freedom values, and absolute transforms for instances with no Mates) of the assembly and switch to a particular named position easily at any time. Keep in mind that the Mate values are relative and are able to be satisfied even if both sides of the Mate have moved.