Other then price, is there a difference (advantage/disadvantage) of using tarp versus REI footprint?

And if it is raining or going to rain, what do you do with your bikes? Do you drape a tarp over it or**********

And if it rained out and its time to break down, how important is it to dry things out? And how do you do that when riding? I have read that some people drape the tent over the bike but I cannot see how thats done logistically.