being able to change the default value is very helpful in the case when you start with a MIDI file that you found somewhere on the internet and that you want to edit using Finale e.g. to repair errors or make changes in various parts of the score. If the original notes in the part you want to change all have a fixed velocity of say 90, you want the new notes to have this value as well to prevent unwanted dynamic variations. Having to change the velocity after you have entered the new notes is a rather tedious and error prone process where you can easily forget to adapt some notes. Being to able to set the default velocity to 90 before making the changes would make the process much more efficient and less error prone.