You want to spoof you mac address if you want to make your computer look like a new computer to the wifi access point. It could be because the wifi gives out free data, but limits it to a certain amount.
Run this command and generate a new valid mac address.
$ openssl rand -hex 6 | sed 's/\(..\)/\1:/g; s/.$//' 26:27:ad:8c:d0:9e
Pass your new mac address to ifconfig and run it with root.
$ sudo ifconfig en0 ether 26:27:ad:8c:d0:9e
$ ifconfig en0 |grep ether ether 26:27:ad:8c:d0:9e