Some pros: Light and small, some are digital and have effects, you can carry most of your sounds under your arm if you are travelling. You can plug directly into a PA. If you don't mind the sound you can record direct with a lot of them, as a lot of them have (mostly lame) cabinet simulators. A lot have headphone jacks for silent practice or recording.
Some cons: you need a seperate power amp to drive your cabs, or an amp where you can bypass the pre-amp, so you carry more gear. If you travel without an amp you take your chances on what you get when you arrive. There is more set-up time if you are playing live unless the stuff is all racked up in advance.
