Within 6 feet of a vulnerable person you absolutely should.

Someone who is infected should be distanced from everyone, and anyone coming within 6 feet should wear N95.

Anyone who has been in contact with someone suspicious for COVID should wear one whenever within 6 feet of others as well.

Outside of those things there's no evidence showing it helps.

It would further help (to some degree) if anyone within 6 feet of someone else to wear them, but that's unrealistic as it encompasses everyone even those not at risk.

Within 6 feet of a vulnerable person you absolutely should.

Someone who is infected should be distanced from everyone, and anyone coming within 6 feet should wear N95.

Anyone who has been in contact with someone suspicious for COVID should wear one whenever within 6 feet of others as well.

Outside of those things there's no evidence showing it helps.