Why bother when I can tether my iPhone and not incur the additional carrier cost.
The addition of the cellular connectivity is so handy for those of us who spend a lot of time away from urban areas. I have owned and still do own a Panasonic ToughBook with the Gobi sled for WWAN connectivity and find it to be extremely hsndy. I'm on a share plan for my cellular data and for the extra ten bucks for the SIM and account you can't go wrong. It is so convenient and I would love to have this multi carrier option integrated into the MacBooks it just makes so much sense.
The city i live in (Tel Aviv) has City-wide free wifi... so for me, this would be useless...