I like to work actual size when I paint, but when I did graphic design (mind you this was a few years ago) the rule was never enlarge the original more than 10% and never reduce more than 15% to void loss in quality.
I can't think of any reason that there is a benefit to working larger than the actual size you want, unless maybe you do highly detailed work and working larger achieves a greater level of detail? My artwork is quite detailed (pay no attention to zombie cat, he doesn't count, lol) but working too large throws off my lineweights, etc.
Hope that helps!