More details about class com.ibm.team.filesystem.common.IFilesystemService in RTC
One answer
The class com.ibm.team.filesystem.common.IFilesystemService is for the below thing eg;
File system view on a team repository. Provides methods for browsing files in arbitrary configurations (workspace, baseline), and for manipulating files in workspace configurations. Also does compare
workspaces, provides workspace conflict report. It is a heavily used class.