SharePoint File System Rules
SharePoint File System Rules deal with the documentation management aspect of your SharePoint environment – excessive documents and folders may degrade the performance of your SharePoint environment.
Fat Document Rules
These Rules check if the total size of fat documents exceed a certain threshold.
Flat Folder Rules
These Rules check if the number of documents in the folders or root exceed a certain threshold.
Note: Having more than 2,000 of any kind of document within a folder or view can cause poor performance.