All United MileagePlus members can now redeem miles for any seat on the plane

When you begin an award search on United's website, a pop-up window suggests entering your username and password before you continue, prompting you to "Sign in to your MileagePlus account to show the best award availability."

The reason? Traditionally, only MileagePlus elite members and customers with a co-branded credit card, such as the United Explorer Card or United Quest Card, had access to every seat on the plane — if there was one seat for sale, those members can redeem miles to lock it in.

Now, that flexibility extends to all MileagePlus members — you don't need to have elite status or a co-branded card to redeem an award, even if it's for the very last seat on the plane.

That's not to say you'll necessarily want to redeem miles when you see the cost — as you can see below, the award cost for a seat on a flight that's almost full can be extraordinarily high — but it's helpful to know it's an option.

Meanwhile, if you are an elite member or have a co-branded card, there's still an incentive to log in before you complete your search. Those customers will continue to have access to additional low-level award availability — in many cases, you'll see a lower redemption rate once you log in.

In the screenshot above, for example, I searched for a flight from Newark (EWR) to Rome (FCO) without logging into my United account. After entering my username and password, the redemption rate dropped by more than a third, since I was able to "unlock" availability held back for elites and cardholders.

United isn't the first U.S. carrier to extend a no-blackout-dates policy to all members — programs like American AAdvantage, Delta SkyMiles and Southwest Rapid Rewards do as well — but it's certainly a welcome benefit, especially if you're hoping to redeem miles instead of booking an astronomically expensive cash fare.