I think it's to allow degrees of speed. if you pick your maximum number of hyperspeed and +0.9 it won't do anything. but if you have a max speed of 5, and you pick 4 and +0.9, you'll go a little bit slower. Doesn't have much use atm, but when combat comes out and escorts and stuff are needed that could be very useful. that's how i thought it was anyway.
Impossible is just a word people use to make themselves feel better when they quit!