When I buy potatoes I am interested to buy 10 kg mass of potatoes, not the amount or potatoes of which has a gravity force of 98,1N. On mars you need to eat 10 kg of potatoes a week, not the amount of which has 98,1N gravity force.

The scales in the supermarket on earth automatically convert the weight into mass for my convenience by applying a constant factor of 1/9,81.

I am hardly far away enough from earth that the constant changed, so I did not need to distinguish between the two measures so far. When carrying the potatoes home I just use the mass of 10 kg as a proxy for the force I need.

And to determine the increased breaking distance of my car, I need to know the mass again.