We advise our customers to not disable the Fast Workspace feature. Since this can lead to instability of the product.
If the Fast Workspace Feature is no longer needed, you can disable it following the steps below:
1. From SharePoint SiteContents click the tile from Collaboration Manager to run the add-in:
2. Click Setup
3. Click Settings, then click Fast Workspaces:
4. Click General Settings:
5. Set the field "Number of pregenerated workspaces" to 0 and save the change:
6. Confirm the fast workspaces deactivation. After that, you will be redirect to the settings overview:
7. To finalize you have to manually remove all the items from the "FastWorkspaces" list. Otherwise the items already created will be used for the creation of workspaces.