Pressing the SPRINT key while falling with a parachute will cause you to fall slower and thrust you forwards further like it did during the Casino Heist mission.

During missions that require you to use and open the parachute, like 'A Home in the Hills', you have to open the parachute or the game won't detect that you actually landed on the roof.
Since it uses the SPRINT key to activate, don't sprint into a save marker while wearing a parachute, because the effect will carry into the save file and if you plan on sharing the save with others who don't have this mod installed, they'll have the effect on their save file permanently though playing the parachute training mission in flight school will revert it back to normal.

Also included the source script if you want to edit the falling and forward speeds. The player can survive falling without opening the parachute if the vertical falling speed is above -20.0 (that is -19.0 or -15.0, not -21.0)