When removing the lug nut from a free-turning wheel using a wrench

1- When removing the lug nut from a free-turning wheel using a wrench,
why is it best to keep the car tire on the ground rather than first jacking it up ?

2- When loading a truck with boxes of varrying weights, is better to load the lighter
boxes before the hevier ones ? Discuss

3- Is it possible to predict the strength and deflection of an I-Steel
beam and when you have your choice of choosing between an I-Steal beam
or L-Steel beam which one will you prefer and why ?