It is desktop software. So your data will be kept on your local drive or network drive.

IF you turn on the optional Remote Data Access feature, then a copy of your data will be sent to the cloud. Anyone you choose to share it with will copy the data from the cloud to their local drive. Changes they make will then be synchronized with the data on your computer via the cloud. So in this scenario, data is on your computer, the other person's computer, and in the cloud. There is no cloud version of Sage 50, so you can't directly access the data that's in the cloud. It's just there for sharing and syncing purposes.