It used to be the case there were lots of places that wouldn't accept mastercard. It's rarer these days, but I still run into them. It would never occur to me to ever travel anywhere outside my local neighborhood without both Mastercard and a Visa. And I realize that 50%+ of the time my Amex (which, of course, is what I need to use for corporate travel) - won't be accepted at smaller places. Expense Report Hell...