Why would anyone want class AB amp when class A always sounds better ?

Inna, I believe you to be quite sincere in your threads and posts which is why I'm responding now.

Whether it's class AB or A, or tubes or SS; the purpose of the equipment is to reproduce "music". As I previously stated, utilizing high quality parts, one would need the hearing of an "Irish Wolfhound" to tell the difference between A and AB. If you have it, fine, maybe it's worth the additional expense; I don't.

The reason for this post is to separate equipment lovers from music lovers. First, in order to qualify for that distinction, (The ability to separate the two) one must be an Audiophile with at least 30 years of experience, and I'll explain why that's  necessary.

In the beginning, we started with our favorite music on the radio. And then we advanced to our own fundamental rigs. They were SS rigs because tubes were too expensive. Those who are still into SS are there because they simply followed along that path to better SS without comparing that to tubes. Or, they decided tubes create distortion.

If you compare the reproduction of a 1K hertz tone, using SS and tubes; SS would win, but that's not music. Music has a certain "Essence" that can only be reproduced by tubes. People who are exclusively into SS are not even aware of that "Essence"; that's because they're not true music lovers. They buy music to hear their equipment, while music lovers buy equipment to hear their music.

Clarification on the above post; SS is OK for power amps; that's because tube power is very expensive when one needs a high powered amp, but tubes are still the ultimate. Here again is the question; can one actually hear "the ultimate".

The Plinius amps of yesteryear allowed users to utilize an A or A/B button on the front of the amplifier to allow for Class A critical listening. The amp generally sounded its best in Class A, but A/B was very close.

I don't know if the current generation of Plinius amps allow for such user friendly options. 

Lower power consumption with most A/B amplifier designs. They tend to be popular in devices like DACs. Due to the nature of the Class A topology, they are very inefficient with electricity and typically generate a lot of heat. My Class A systems can only be run once or twice a week...otherwise my power bill will go up! 

Class A has a conduction angle of 360 degrees, whereas A/B is less.

In theory, this should translate to a more controlled and linear amplification of the signal. In most cases, Class A amps have more of a "grip" on the signal and can be "straight wires with gain." Everyone hear probably knows what I mean (see what I did with that spelling mistake) lol 

yep. So class A is superior if it is designed well without compromises.

Orpheus10, I don't have such a hearing as you imply, but my ear is quite sensitive to some aspects of a sound. 
Let's not transform this thread into tubes/transistors debate. Sure, ultimately tubes rule.
That's what we are trying to talk about - designs without compromises or almost without compromises. Heat, space, cost, look - this is all BS, just certain side effects. Done right it should always be full Class A design. And since Class A requires high level power supply, that's an additional advantage, that's where it all starts - with a power supply.