Positive
A soldier doesnt need much skill to operate a gun or cannon as he does to use a bow or sword, also, mining was made more efficent because miners could blow up the caves and find more metals, and ships could attack each other from a distance using cannons and firearms.
Negative
It caused more wars over supplies and ammunition, also, some weapons could detonate accidentally, many people are killed by guns and explosives, they have developed into weapons of mass destruction and can destroy entire cities.