Business travelers will be forgiven for shrugging off the hype surrounding the announcement that British Airways and Iberia of Spain were merging. After all, the flag carrier airline of the United Kingdom has flown from one potential partner to another for 20 years.

Back in 1989, British Airways announced plans to buy United Airlines. It never happened. In 1992, it struck a deal to invest $750 million in US Air. It never happened—US Air became US Airways, tried to merge with United, and eventually did a deal with America West in 2005. BA made at least two serious runs at KLM, the Dutch carrier that merged with Air France in 2004. Last year, it was going to be British Airways and Qantas, the Australian carrier. And after twice failing to gain approval for a wide-ranging antitrust deal with American Airlines, BA is currently trying again, this time in a menage a trois with Iberia.

It's easy to laugh at the corporate travails of the carrier that once claimed to be "world's favorite airline," but BA's careening from partner to partner is hardly unique. Merging—and talking about merging—is what big airlines do instead of running a tight financial ship, turning a profit or, heaven forfend, focusing on customers.

"I compare it to two drunks, where you assume that if they hold on to each other, they will walk straight," airline consultant Adam Pilarski told Time magazine over the weekend.

Pilarksi's metaphor, gleefully echoed in snarky statements issued by two of BA's low-fare competitors, is apt. BA and Iberia have lost a combined $800 million in the last six months, and both face potentially crippling strikes in the coming weeks. Delta Air Lines, which merged with Northwest Airlines last year, and American Airlines are money losers too, but they're both pursuing Japan Airlines, the cash-consuming giant of the Asian skies. In Latin America, Avianca of Colombia and TACA, a consortium of Central American carriers, last month announced their own merger. The chief executives of US Airways and United Airlines, which have been bankrupt a total of three times this decade, have also tried to arrange mergers.

What drives the urge to merge? The chimera of cost savings. At least on paper, merged carriers can slash back-office, information-technology, and fleet-maintenance expenses. They can share airport facilities such as check-in desks, gates, and passenger lounges. Joint procurement of everything from airsick bags to jet fuel saves money. Merged carriers can eliminate duplicative routes and shed excess aircraft, thus giving them leverage to drive up fares. For their parts, BA and Iberia claim the merger will generate $600 million in savings by the fifth year.

And then there is the oft-repeated cliche, trotted out during every merger announcement, that bigger is not only better, but inevitable. Or as British Airways chief executive Willie Walsh said last week: "Consolidation is happening in our industry, and it is critical that BA starts participating in that."

In practice, however, bigger isn't probably better, and the promised cost savings rarely add up. Thanks to its purchase of Northwest, Delta is now the world's largest airline, and it originally promised upwards of $2 billion in merger-related savings. But the payoff has been diluted because the labor groups at mostly nonunion Delta and mostly-unionized Northwest haven't been harmonized. Nearly five years after the merger that created what we now call US Airways, pilots who once worked for the old US Airways and pilots from the former America West continue to squabble amongst themselves, in the courts, and with management. They still haven't reached a contract agreement.