Difference between Executefile and loadfunctionlibrary in QTP

With executefile, we can’t debug the statements. 
With loadfunctionlibrary, we can load multiple library files separated by comma and we can debug as well. If you want to debug, you can associate files with action.

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In execute file ,we will execute .vbs,.qfl,.txt files but in loadfunctionlibrary only we associate .qfl files why because this mechanism introduced in qtp 11.0 version
executefile "path.qfl"
executefile "path.vbs"
in load fucnction library we jst associate the qfl files