In the old days, if your let your tires sit on cold concrete for months at a time, they would develop flatspots. Today they are virtually unheard of.
Also, you want to keep a load on your suspension components. After all, the parts are designed and engineered to be used under load at all times, taking the weight off springs and shocks (or struts) is usually worse than leaving weight on them. The suspension of the car should remain compressed as well to avoid the onset of rust. Springs
can take a set, but not as much as years ago; the steels that are used today are far superior and unless the time span is long, blocking to save the suspension and springs is probably not necessary for the couple of months of the winter.
Of course, we who have the fiberglass springs don't have that concern in the first place.
Suspending the car to take the weight off is more a consideration of the bearings. This can be avoided by simply rolling the car back and forth a few times a month.
As for the reasoning behind keeping the load off of a radio-controlled car... It's beyond me - never raced 'em.
