You may not be missing anything. Wi-Fi allows you to access the internet without using any Data from your plan. If you have an Unlimited Data Plan this makes no difference.
Wi-Fi may also allow faster connection speeds depending the speed of your home internet signal vs your 3G signal.
Wi-Fi may also use more battery life if your phone is constantly looking for a strong Wi-Fi signal.
In the end, it is a personal preference. I like using my Wi-Fi because I get a stronger, faster signal in my house vs. 3G most of the time. (I live in rural West Central MN.)
Thanks for the info guys. I think I'll just stick to my computer for my home WIFI Besides-it has a bigger screen!