Certain cmdlets in the SkypeForBusiness PowerShell module appear to have the need to write temporary files to the $env:temp folder in order to correctly function.
Over time, disk space consumption can add up, particularly when this path points to the default location, namely on the same drive where the operating system is installed. Needless to say, regular manual or scheduled clean-up of the temp directory is generally recommended to ensure continuous and trouble-free operations.