The pros would be system tweaks like 5 icons on the dock, infinite icons in a folder, themes, etc. There really aren't any cons, although when you jailbreak, you do remove the high amount of protection that Apple puts on all devices. It's really rare to come across something that may be harmful, but there's the chance.
A jailbroken device doesn't effect other devices on the network, although if you happen to come across a security breach (which is very rare), theres a chance it could put personal info, etc at risk. When I say rare, I mean very, very rare. It's not often that you hear about an iOS device getting a virus or a situation where a jailbroken device messes up a normal one. It's probably never happened so I wouldn't worry at all.
There are millions of people who have jailbroken before and 99% of them probably have never had any issues before.