The matched sets are intended to keep the bias current through both or all 4 of power tubes close to the same current. That minimizes the hum from the B+ ripple that is on that first stage of the B+ voltage. Earlier stages in the pre-amp have more filtering, so they are more DC and less AC ripple. But the B+ that goes to teh Output Transformer, and then the power tubes plate voltage, has a couple of volts of AC ripple. But in a push-push amp configuration the ripple current on each tube cancels out the ripple on the other tube, provided they are matched.
Some amps have separate adjustments for each tube, so you don't need to buy matched tubes.
Just because you don't have an adjustment for the bias current, doesn't mean you don't need one. It also doesn't mean you can't adjust the bias. I have changed resistors to fine tune the bias in fixed bias amps without adjustment pots, and also in cathode biased amps, where the current was just not acceptable. The Egnater Tweaker 15 is cathode biased, but was set way too hot, so I had to change the cathode resistor. Most Blues Jr's are also too hot, even though they are fixed bias, there is no pot to adjust it. Mt Fender Princeton also does not have an adjustment, but the bias current was OK last time I checked.
Some of the newer amps have computer controlled biasing. I believe the newer Bugera Infinium has that. and so does the The Fender Bassman 100T I have and the Hughes and Kettner Tone Meister 15W. In those amps you don't need to worry about matched tubes, or adjusting the bias at all.