there's actually no significant value for it.
it's more of a comparison field.
in colissions (stock BC) the lower mass object gets bounced off the higher mass object. the difference between them, plus the speed and direction of the incoming object gives the value of how far and how fast the lighter object will bounce.
in KM that was replaced to give a Nemesis style of colission, without bounce, but rather a dampened crash.
to give a good setting, it all comes down to acceleration and angular speed.
10 of max speed will give around 5600/6000 kph at full impulse, at 100% power.
10 of acceleration means reaching 10 of speed at 100% in about 3 or 4 seconds.
(by eye-o-meter, after using MPE a LOT

)
have in mind that even the lighter ships are about tens or hundreds (or even thousands) of metric tons. the bigger ones are about tens of millions. starbases are off billions or more 0.0
(on a quick balance guide, I set the Galaxy as Mass=4600. it weights 4600000 metric tons. using memory-alpha or another trek database, I got the relations for other ships by using Galaxy=1)
dunno, MLeo or Mark correct me in the colissions part....