It comes with a balance knob?!?! I'll take it!

I had an ARC Reference 1 and Reference 3, both of which had balance controls. Despite symmetrical set up, the sound in my room pulls slightly to the left. The balance control worked exactly as it should and was very useful. 

If you ever had a multi tubed preamp or integrated, you would find out very quickly as to why a balance control can be so important. 

I damaged my right ear drum at a Hot Tuna concert back in the '70's when  "The Wall of Sound" was popular (so why only the right ear you ask? It was at the Rutgers College Basketball arena and I was sitting on the right side with my right ear up against the speakers on that side) Anyway, it sometimes helps to make the right channel just slightly louder then the left. It's also the reason I like having defeatable tone controls. It may not be "pure", but it's all about the enjoying the music. 

I make a headphone amp with a balance  control. I had one customer ask for it just because he thought he needed it, and another that has a hearing problem in one ear. Depending on what he's listening to he has to adjust balance. 

Turned out to be a bit of a selling point.

Balance control makes sense even if hardly ever used in my case. It is God sent for hard of hearing in one ear, and may even be advantageous for normal hearing folks to better center the sound on some questionable recordings. More options is always a plus.