Here is a scenario when it would be useful:

I want to use a click to heal system. Let's assume I'm using Vuhdo since that's probably the easiest to configure. I'd set up some profiles:

-Holy profile: cast flash heal on a right click.
-Shadow profile: cast Power Word:Shield on a right click.
-Resto Druid profile: cast Nourish on right click
-Tank Druid profile: cast nothing on right click

Depending on what team I want to use, I have to first create all the profiles, and then make sure I load the correct ones on each toon.

Here's how I would like it to work with ISBoxer.

A left click in a repeater region is recognized. ISBoxer knows to do the following, based on the repeater region and the type of click (let's say right click somewhere in that region):

Do Key Map Mouseover Flash Heal -> Holy Priest ATG
Do Key Map Mouseover PW:Shield -> Shadow Priest ATG
Do Key Map Mouseover Nourish -> Resto Druid ATG
(if we dont' map it then it won't do anything for Druid Tanks, as intended)

Now I can mix and match teams with ease while allowing ISBoxer to take care of my mouseover healing.
Note that all those keymaps have the target=mouseover in the macro. Otherwise they're just regular macros we use all the time in ISBoxer.