[Unsolved] How to use "leading space"? What do you usually adjust "leading space" property for?

When I need to adjust local horizontal spacing, most of time I use the "layout stretch" commands ( curly brackets { and } ) . When I need to enter virtuoso/cadenza, I mutate bar duration and enter notes and adjust their "leading space" properties in the inspector/property panel to pack them tighter horizontally. I'm using computer keyboard entry so adding "grace note object" and adjusting pitches is quite counterproductive.

1. By method of trial and error, I found out the best values to use range from -1 to 0. How is the value used to calculate the final spacing result?
2. What do you usually adjust "leading space" property for? rather than using "layout stretch".

https://musescore.org/en/handbook/4/properties-panel#appearance
https://musescore.org/en/handbook/4/formatting