When DropSync performs a sync with a synced place it initiates a separate connection for each synced item. The maximum number of simultaneous connections property controls how many such connections are allowed to run at the same time. Depending on the physical characteristics of the synced place (eg an ssh accessible host, local hard disk etc) a larger or smaller value for this property can result in better or worse syncing performance
To set the maximum number of simultaneous connections for a Synced Place: