If used in global combat and warfare, they have the potential to wreck havoc on the earth's environment and possibly severely affect the ability of this planet to sustain life in the future. Nuclear weapons are also rather difficult to create and use, as they do contain a lot of energy within that metal shell. My belief is that they should not be used.
Nuclear warfare is completely and utterly useless. If anyone engaged in nuclear warfare they would immediately be attacked with nukes who would then counter with nukes, turning Earth into a smoking pile of radioactive waste. The only reason we keep nukes is for this theoretical war so that no one nukes us. If you have ever seen War Games or played Global Thermonuclear War you know that you cannot win. It is impossible. The whole point of that game was to show that nuclear war is pointless and so we should all stop threatening with nukes. It only results in the end of all living things.