This parameter is applicable in RPC protocol only. Scanning files over the network can cause network congestion. You can choose to scan files in-place on the RPC client share, thus improving the overall performance.
The FilerPerformanceThreshold parameter allows you to specify the file size threshold value below which the file is copied from the RPC client share to the Protection Engine temporary folder. Hence, to ensure that most of the files are scanned in-place, you must enter a threshold value lesser than the average file size in your environment.
The FilerPerformanceThreshold parameter accepts value in bytes. If you specify the default value (0) then all files are copied to Protection Engine temporary folder and then scanned.