This tool is a wonderful tool for checking PDMS/E3D model for any Connection Compatibility.
As we know, in the PDMS/E3D all Components must be connected to each other, so in the PARAGON there is CCTA table (see PDMS/E3D Help for details) that specify which Connection can be connected to which Connection, like FBB-GBB for connection between flange and gasket.
Sometimes because of problems in the CCTA table or maybe by mistake, Designer create a component which is not compatible with the previous one, so PDMS/E3D return an error then create a spool with 100mm length. Then user just for continuing his/her job, uses FCONN command or set the Distance to 0.0 to connect those components. So before any important issue of Isometrics or MTOs, it is recommended to check these Incompatible components.