The master cylinder piston only moves a fraction of an inch to compress the brake fluid to move the pads against the rotors. This area of movement in the cylinder piston gets highly polished. When bleeding the brakes, the brake lever can be pulled all the way to the bar. This pushes the cylinder piston past the polished area. Depending on the age, there may be a rough area or even a lip that can snag or scratch the piston seals. As pads wear down, both the master piston and caliper piston(s) will move into these unpolished areas.
I'm very careful bleeding my brakes, especially my older bikes. Speedbleeders wouldn't save me any time on the rear, but would probably save me a minute on the left front caliper. If speedbleeders make riders bleed their brakes more often, more power to 'em. I've never tried them or the vacuum. But aside from checking the oil level, bleeding the brakes the old way has to be one of the easiest maintenance chores. Don't even have to lie on your back under two tons of steel like when doing a car.