Question

Imagine if spherical mirrors are not known to man what are the consequences

Answer 1

1. Substitutes of headlights of cars should have to be found.
2. Dentists has to use any other tool to observe the teeth.
3. People will have to shave their beard without using mirror.
etc are the consequences.

Answer 2

If we did not know about spherical mirrors maybe doctors could not view our organs like teeth,ear,etc.(doctors use spherical mirror fixed on spoon-like structures to focus light).
Streetlights would have to be maximum as there was nothing that a single light can diverge.
The rear view mirror of cars would not be there and the drivers would have to think of a new method to solve that problem.

So we have a lot of advantages on the discovery of mirrors.