The obvious pro is you can mint while keeping your spending private keys offline.
Most cons are speculative:
It introduces a change in the protocol that we would have to support forever. It may add development work if it’s broken or during other changes like bitcoin merges. It adds a new script opcode for which I had to pick a number, and this number may conflict with a future feature in bitcoin. I think that’s the reason it hasn’t been merged into Peercoin yet. The problem is less important for Nu and B&C where we already made a lot of changes in the protocol.
It may increase centralization because some people may pay service providers to mint for them to a point where a few important actors mint most of the shares like Bitcoin pools. I think that’s the reason why Jordan didn’t want to include it in Nu. I don’t think this will happen though, because it will be easy to set up your own cold minter and because contrary to bitcoin you can’t reduce the reward variance by pooling your shares. (That’s what I chose in my implementation at least, it’s also possible to make a version that makes variance reduction possible). And in Nu and B&C that would also mean giving your votes to the provider.
Some people think careless users will just publicly release their minting key hoping someone will mint them. But it would not work with my implementation because the person minting could burn the reward, and if more than 1 person is minting the same shares the resulting blocks will be rejected.
I also made some technical choices during implementation that may have pros and cons (and alternatives with different pros and cons), but that’s probably out of the scope of your question.
It’s also not finished yet. The Peercoin version lacks the GUI changes to handles cold minting addresses, and it would require some changes to be implemented in Nu and B&C. There was also a suggestion on the Peercoin forum to add support for multisig spending keys. I think it’s a good idea and the implementation should be changed to support that (it’s not a big change).
If you want the full story you can read the long peercointalk thread here: https://www.peercointalk.org/index.php?topic=2783.0