The second one allows (but doesn't require) you to enter separate values
for the width and height factors. For example, you could simultaneously
reduce width by 0.6 and enlarge height by 2.5, but if all you want is
enlarging both by the same factor, just enter one value.
AFAIK, it seems to work on all objects, including groups. It will work
after a fashion (it won't crash) with a collection of selected objects,
but only one of the objects is resized.