Ordinarily the workspace folder (which contains data source configurations and a snapshot of the source data — i.e. the last set of data that was retrieved from the database) is stored locally on each machine. This is how the majority of users use EasyCatalog. If the workspace folder is stored locally and one user changes a field option this change is not reflected on any of the other machines.
The ‘Multiple Users’ checkbox allows the workspace folder to be stored in a central location (and opened by multiple users), while the snapshot of data is stored locally on each machine.