Having Nightly/Snapshot code available lets users adopt new changes as soon as they are made, and can give feedback of any bugs or exploits. This gives the user the choice to either have the latest version of Pumpkin, or one that is more stable.
Once a snapshot is widely confirmed to be free of deadlocks and *bugs, it will be merged in production code.
*by bugs, I mean ones that weren't present in the main code, and only exist in Nightly.
(This would also help plugin developers know about changes ahead of time, so they can prepare for updates)