When I ring up a big bill at the grocery store, I picture myself in a Delta Comfort+ seat. That's because I'm paying with my Delta-branded American Express, where all dollars spent add to my SkyMiles bank (which I tend to use for upgrades).

I am a fan of the airline's SkyMiles program and the American Express card that pads it. That puts me at odds with others who find my approach old-fashioned or best reserved for business travelers whose companies pay the way. Those people probably don't live in a market with a carrier as dominant as Delta.

"For Minneapolis-based fliers, having a co-branded card can make a world of difference. Perks like free checked luggage can easily offset a card's annual fee," said Kyle Potter, editor at Minneapolis-based Thriftytraveler.com. Fliers with a gold ($95), platinum ($195) or reserve ($450) Delta-branded American Express can check a bag for free; the airline charges $30 one-way on many flights.

And what to do with those miles you rack up with the card? I've used them to fly to Hawaii, for upgrades, and to partly pay for a flight. Delta's unique Pay with Miles feature allows SkyMiles credit card members to pay for a flight partly with miles. (Any SkyMiles members can do the same using the similar Miles + Cash program.)

Potter's favorite way to use SkyMiles is to nab a flight during a SkyMiles flash sale, when the number of miles to purchase a flight can be half of the usual charge. "Last month they had a round trip to China for 30,000 SkyMiles," Potter said. Those sales, though sometimes unannounced, are often noted with an e-mail to SkyMiles members.

Potter explained that because Delta has such a hold on our market, other airlines can drop fares to bring in customers and Delta won't necessarily follow suit. "Because they do have those loyal [business] fliers, there is not the pressure to force them to cut prices."

When dealing with a behemoth in the marketplace, book the best fare on any airline, and avoid becoming a slave to Delta in the search for SkyMiles. Especially when a trip to the grocery store will tick up the miles.