one use of this feature is it could lead to the ability to create a mission where you are a "men"unit and have to dive to get to the SDV (to complete the objective and move on to whatever the next objective may be)
it could also allow for making a mission where you start under water instead on the surface near enemy units (to do whatever the objective is) this will allow you to be undetected when starting/spawning(because starting on the surface as a SDV with enemy units nearby will lead to you being spotted)