As a team working over the mark is easier, as is removing the goods. But to work as a team you have to be able to reasonably trust your partener, or parteners. If you can't trust them then the scheme won't work.
A solo pickpocket works alone, and has to lift the mark's wallet on their own. A "cannon" can work in secret and vanish leaving no trace behind, but they have to work to find the right place to make the lift. A solo also has to carry the wallet away with them, instead of having a partener to pass it off to. A bonus is that a solo pickpocket doesn't have to share the profits, but having help is always good too.
This guide has tips for both solo and team pickpocketing, so you're set either way.