how to use scaleX and scaleY props

what is the right way to use the scaleX and scaleY properties? I don't quite understand how to use them...

right now, I'm using this, but I think scaleX and scaleY would be a better idea:

Code:

---

if(condition){
some_mc.width++;
some_mc.height++;
}
else{
some_mc.width--;
some_mc.height--;
}

---

scaleX and scaleY are the percentage of its original size that you have blown up/shrunk an object. It is on a 1-unit scale. If scaleX == .75, the object is 3/4 as wide as it originally was.