Hi WhySoTough
You're question is a good one in that many bus pilots ponder the same question.
After fifteen years of being a bus driver I'll give you the skinny on that table.
First of all the chart depicting Vapp determination with speed additives is purely in place if you experience dual FMGS failure and have no Vls speed depicted on the MCDU perf page. It's good To know its there and as others have explained know how to use it but it's purely backup. Use the Full flap VLS for speed additives after Youve properly sequenced the flight plan with correct destination.
The landing distance requirement is exactly what it implies, since you are increasing your approach speed due to an abnormal for example, you're checking on how much runway your specific malfunction requires you to safely land on. With any abnormal you would use the Config full "Autobrake Off" landing chart ( for maximimum braking effort after landing ) to determine your landing distance.
Hope this helps.
T
Last edited by Trust me Im Staff; 9th Jun 2012 at 08:20.