[in menu Analyse]
This operation checks if current MIDI file contains notes that are not stopped (a note on command is missing note off command). It considers pedal commands hold and sostenuto and all-notes-off. When such notes are found then the operation offers to stop those notes or remove those notes.
Hanging notes cause that polyphony increases unnecessarily and depending on the used sound it can be heard. The notes are on till end of song, some sounds are fading out earlier so that the problem might not be noticed. Such notes are usually unwanted bugs in MIDI files.