The trifold mirror was a genuine invention rather than a decoration. A single mirror shows you the front of your face and nothing else, which is fine for shaving and useless for dressing hair or fastening anything behind you. Hinging two narrower panels either side, angled inward, puts your own profile and the back of your head into view at the same time - and because the angle can be adjusted, you can set it to whatever you are actually doing.
It became standard on dressing tables in the nineteenth century and then disappeared from most modern ones, largely because a single flat mirror is far cheaper to make and to ship.
Our master Indian artisans build the side panels on the same arched profile as the centre so the three read as one shape when they are closed up, and set the hinges so the panels hold whatever angle you put them at rather than swinging back. It is a small mechanical detail and it is what makes the mirror worth having.