Question

What is the use of convex mirrors?

Answer 1

Main purpose of convex mirrors is to widen the angle of view.

Explanation:

Of course they make the image smaller as compared to a plane mirror, but the angle of view is greater.

Most outside rearview mirrors in cars are slightly convex, so the "death angle" is reduced. It does make the cars beside/behind you look farther away, so a compromise is struck.

In shops, convex mirrors (large ones) are often employed to give the shop personnel a better view of what costumers are doing out of the line of direct sight.