I realized the difference when I took my wi-fi only iPad to a restaurant. Could not look up anything on the Internet. However, I could look up info on the net using my iPhone. If my iPad had cellular and I hooked it up to my T-Mobile cell phone account, I would be able to access the Internet anywhere my iPhone can access the Internet because I would have cellular data available to me when wi-fi isn't available. If I wanted to, I could use a cable to connect my iPad to my iPhone to allow my iPad to access my cellular network, but nobody (except college students on a budget) wants to do it that way. If I had it to do over again, I would have paid $100 more for cellular. It's not something I would use often, but would be very nice to have. iPads last for many, many years so the investment is amortized over time.