Do you need to multiply or to rescale? That's the question.

At first glance there is no discernible difference between Multiply by and Rescale to when the same percentage is used. Take a basic InDesign document containing a set of square frames—as below—and stretch the width of every object by 120%.

A simple set of squares to be resized through Equalizer.

Whatever the task you select in Equalizer (either Multiply or Rescale) this apparently amounts to applying a factor of 1.2 (=120%) to the considered dimension.

120% factor applied to the widths.

But there is a tiny difference that may become huge depending on how InDesign deals with scaling in your current config. Technically, setting the scaling factor of an object alters some transformation attributes without actually changing its intrinsic size. By contrast, resizing an object is about changing its inner geometry and does alter its inner dimensions.

Now, InDesign has a general preference which is turned on by default and automatically translates any scaling operation into resizing:

InDesign “When Scaling” preference.

• When the option “Apply to content” is enabled, objects do not retain their scaling factor because every time you apply some percentage to a dimension (say 120%), InDesign interprets it, in fact, a resizing factor. So it resizes the object and instantly resets its scaling attribute to 100%. In other words, the above squares become actual rectangles.

• But, if “Adjust Scaling Percentage” is selected instead, rescaling is no longer equivalent to resizing. Our squares remain intrinsically square, they just appear rectangular as a transformation effect acting onto their width (adjusted to 120%.) In such case you can see—in both the Control and Transform panels—that InDesign remembers the applied scaling:

When adjusted scaling percentage remains visible.

Equalizer just works with respect to InDesign's preferences, so the actual meaning of the Rescale task is up to you. There are cases where your documents want to use persistent scaling percentage for containers, and then the script will allow you to reset the scaling to some uniform value, while Multiply would resize the shapes by the desired factor.

Furthermore, inner objects such as graphics or imported pages always retain their scaling percentage whatever your general preferences. Here the difference between Multiply and Rescale becomes obvious (click to see the full anim):

Multiply vs. Rescale applied to inner graphics.

Equalizer is smart enough to process Multiply by and Rescale to as two distinct tasks, and it can even resize one dimension while rescaling the other. So check your InDesign preferences, adjust your eQ settings accordingly, and you'll get the exact result you expect.