Field help (FLGLIEN) 

This checkbox is automatically activated and cannot be modified if a link of type "To Financials" has been detected on the Fixed Assets V5 folder (the folder is linked to an X3 Financials folder).
If no link to an X3 Financials folder has been detected, this box is not activated. It is nevertheless necessary to activate it manually if the Fixed Assets folder is managed with an X3 Financials folder and if, for various reasons, this link has been deleted

In effect, when it is activated, those objects shared with X3 are not retrieved by the migration processing. The list of these objects is given in the FRP Fixed Assets migration documentation.