AT&T (NYSE:T) sports one of the slowest-growing dividends among the 30 Dow Jones Industrial Average (DJINDICES:^DJI) components. Over the last decade, AT&T's payouts have grown by an average of 3.9% a year. At the other end of the spectrum, fellow Dow member IBM (NYSE:IBM) juiced its dividend by 20% a year. Closer to the Dow's average dividend growth, United Technologies (NYSE:UTX) payouts have increased by 13% annually.

T Dividend Chart

T Dividend data by YCharts.

From this popular and often useful perspective, AT&T's dividend appears to be a total dud. It's trivially easy to find high-quality companies (aka Dow members) with drastically higher dividend growth rates.

But that doesn't necessarily make AT&T useless to income investors. You see, the telecom giant had a running start heading into this decade-long comparison.

Ten years ago, United Techologies shares came with a 1.4% effective dividend yield. IBM sat even further back, with a meager 0.8% yield. AT&T soared high above both, with shares yielding a 5.7% annual dividend payout.

In fact, neither IBM nor United Technologies have come close to AT&T's massive dividend yields in the last decade. It's not for a lack of effort, as the chart above shows. AT&T's head start was just that big.

T Dividend Yield (TTM) Chart

T Dividend Yield (TTM) data by YCharts.

How has this trade-off between slow dividend growth and high starting payouts worked out for AT&T investors? Quite well, I'd say.

Without dividends, AT&T shares have lagged far behind the Dow's returns in the decade-long period we're talking about. Not by a huge margin, historically speaking, but enough to make the difference felt in your portfolio:

^DJI Chart

^DJI data by YCharts.

But if you reinvested AT&T's payouts along the way, the story changes. From this angle, AT&T investors haven't lost out to the Dow for many years -- even if you ran the Dow through a DRIP plan, too:

^DJITR Chart

^DJITR data by YCharts.

So AT&T's large dividends have tripled investor returns over the last decade, and they make the difference between beating the market or not. IBM's generous dividend growth has only produced a 33% boost to Big Blue's plain share price returns. United Technologies provided 36% of its one-decade returns in the form of dividends.

That's not to say that AT&T is the perfect dividend stock. Reliable long-term payout growth is important, and Ma Bell's yields will eventually fall below many of its Dow peers unless the company makes a serious commitment to greater dividend boosts. Plus, past performance is no guarantee of future returns.

But keep this value-boosting payout in mind if looking for large-cap stocks with a solid dividend history. Warts and all, AT&T's big payouts have indeed helped its investors beat the market.