The adjustments help you balance slightly unmatched valves, and let you set the bias for valves to account for the manufacturing differences between different makes, and even different designs and batches. class A, class AB, class B then small bias adjustments don't change the sound much in my experience. If you're not changing the bias so much that you alter the class of the amp, i.e. I find it makes more difference to the sound when you change the bias on preamp valves, but they aren't the ones that you typically adjust in a commercial amp, it's the outputs. I have built many valve amps (I know weird, but I love the technology) and experimented with bias points. OK, but I only question the need for pinpoint accuracy, and this gets back to the OPs question. ARC still use manual bias for example it's not like they're unaware of the (ancient) technology behind autobias.

The reason for bias in the first place is for optimal performance. Autobiasing isn't as accurate as manually biased and.

Check bias guitar amp tubes