purchasing airline tickets

None, unless the airlines goes belly up.

If your credit card has any rewards plan you will get credit. If you are booking with a third party rather than directly with the airline it will allow you be sure the airline actually is holding the seat. Once you have paid for the ticket you should get a confirmation # that you can use on the airline's website to make sure. Don't pay the CC bill until you see it.

Depends on your credit card. One of mine has 'baggage insurance' if the luggage is lost they pay what the airline doesn't. (I have never used it and don't actually use that card for travel so.... it's kind of worthless, but... you asked :) ) So you would have to check with YOUR card issuer and see if they offer any "perks' That said I pay with a credit card because I tend not to trust airlines, rental car companies and hotels with access to my CASH like they get with a debit card. If they screw up and double charge me, for example, then my cash isn't tied up while I fight with them!

Credit card is the way to pay for any flight. I once was stranded in Britain after my airline went out of business, and a charge back might have been warranted had I not hitchhiked back to the U.S.

Unless you are going to an airport to buy the tickets, or have a travel agent working for you, cash is out of style. On-line sales require cc. There are plenty of supposedly protective clauses buried in your card's fine print so it is worth getting out a magnifying glass. For instance, an airline cancelled part of an international itinerary while I was on it which cost me several hundred dollars. Upon return, I put in a claim for non-delivery of service on the cancelled flight. I did get a refund from the airline. Full disclosure: I complained to several agencies involved with the airline, inconveniently functioning in Chinese, so I can't say for sure which gesture moved the mountain. But it can't hurt to try.
Now a question for you: Is there any advantage to NOT using a credit card? Especially living in Canada, you can earn points on various loyalty schemes. My long Chinese trip bought me some groceries through my President's Choice card even before the trip started.