It gives you way more storage as your Edge only has 4GB but only 3GB is allowed so for example if you have a lot of PDFs then I would advise you to get an SD card but if you don't have much then don't worry about it. I rather keep all my stuff in the SD card as if you use too much space on the Internal Storage it might crash the system. Don't know if it does or not don't want to try LOL.

Since, those SDHC cards are like dirt cheap I got a bunch of 8GB SDHC cards last Boxing Day for like 10 dollars each.