Level matching is important if you want to minimise or eliminate an important factor not related to actual, qualitative differences between components. This has been proven so many times over decades that it really shouldn't be contentious any more.
How far you take these things is entirely up to you, the listener, and what hinges on the result of the listing comparison.
Not everyone has the equipment or inclination to match down to 0.1dB, but some attempt to match levels such that a perceptible level difference doesn''t exist costs nothing but a few seconds and at least minimises a known influence.
Most people of course make no attempt to level match whatsoever, and will even attempt to draw meaningful conclusions when comparing equipment in different locations at different times!
This is why perhaps 95% of subjective comment about audio equipment is quite frankly, nonsense.
I would go further and suggest that audible differences often don't exist between boxes of audio electronics, and that reported differences are actually the result of the poor comparative listening practices.
Unfortunately, lack of proper listening controls are essential to the practice of many manufacturers and dealers selling people new, improved, upgraded, tweaked, special edition, equipment which performs much the same as the preceding generations of equipment. So we should not attempt to persuade the industry to change tack on this issue, but those individuals wanting to improve the reliability of comparative listening can benefit form a little extra care taken to reduce bias.
