A megapixel is one million pixels. A pixel is a picture element. So 7.2 is 7,200,000 pixels.
What does that mean to you? The larger the file, typically the bigger the print, or the closer you can zoom, cut, and edit without pixelization.
This is a nice link that equates to picture print sizes bases of pixel count:
http://www.digicamhelp.com/processing-photos/printing/print-size.php
If you don't plan on printing larger pictures, or editing the picture to only print a part, larger pixel counts can mean higher cost.
7.2 is pretty standard nowadays, and I would think a decent enough number depending on your needs.