If you have a Cuttlebug, BigShot/BigKick/Vagabond, or Grand Calibur then no you do not need one.
If you don't have one of the above machines and you are absolutely certain that you only want to emboss and not use any Nesties or other dies, by all means get it. It's a good machine that does exactly what they advertise.
If you think you'll want to use cutting dies, save your money and get one of the above-mentioned machines instead.
I have one and I used a 50% off coupon at M's to get mine. Now that I just got the Big Shot, not sure if I will be using it much. But, it does do exactly what it says it will. I have used it several times. So, like another poster said, if you don't have any other machine that will emboss, then this is a good option. Plus, with a coupon it would be very good deal.