MAC address should be unique for each network card - whether it's wireless or wired. It's this uniqueness why some networks will use it to distinguish an authorized user from the unauthorized one. If you ever had a time-limited access to the network, chances are that your MAC address was used to block you once time is up.
I will leave it up to you to think of scenarios but I find randomizing my MAC address a useful option in Linux. Therefore, I created a script to automatically generate a new one. This script will randomize the last three octets of the MAC address while leaving the first three octets as they originally were. In effect this makes your computer present itself to the network as the new adapter from the same manufacturer.
Script#!/bin/bash
INTERFACE="eth0"
CURRENT_MAC=`/usr/sbin/ifconfig $INTERFACE | grep ether | awk '{print $2}'`
ORIGINAL_MAC=`/usr/sbin/ethtool -P $INTERFACE | rev | cut -d' ' -f1 | rev`
ORIGINAL_MAC_PREFIX=`echo $ORIGINAL_MAC | cut -d: -f1-3`
NEW_MAC="$ORIGINAL_MAC_PREFIX`/usr/bin/hexdump -n3 -e'3/1 ":%02x"' /dev/urandom`"
echo "Current MAC : $CURRENT_MAC"
echo "Original MAC: $ORIGINAL_MAC"
echo "New MAC ....: $NEW_MAC"
sudo /usr/sbin/ifconfig $INTERFACE down
sudo /usr/sbin/ifconfig $INTERFACE hw ether $NEW_MAC
sudo /usr/sbin/ifconfig $INTERFACE up