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

I would not live without balance, and I love remote balance via my chase Remote Line Controller RLC-1 which gives remote mute, volume, balance, and tone controls.

The better your system is at imaging, the better it reveals any imbalance: I occasionally find tracks, especially compilation discs with many engineers involved, benefit a LOT from a VERY SMALL balance tweak. 

All center, all imaging is Phantom, all engineers equipment, hearing, specific day's performance is perfect or a bit less than perfect.

Your system, tubes, connections, move something, disturb something else, a slight imbalance can occur, easily resolved until you go thru and re-check everything.

Imperfect space, best compromise, yes indeed.

Lots of people with an imbalance in their hearing. Let’s not make gear that only 20 somethings can use well.  Speaker positioning is another reason.  You may need to put your speakers in less than an ideal situation and the balance knob will help.

I for one am really happy to have balance, loudness and tone controls. 

just discovered

acoustic research made a variation of remote volume, balance,

I prefer the Chase 4 inputs and 2 outputs

Typically the better the equipment the less adjustments there are as each has a negative sonic impact. Balance is something nearly all high end equipment has. As @erik_squires pointed out the speakers could have on confined space on one side and open on another, so to have the soundstage centered balance control is needed. Also for people with differential hearing. That is the only control on audiophile gear… the designs to put sound quality first will not have tone controls.

I think all Lamm pre-amplifiers come with "balance" adjustment, in the form of a volume knob for the left channel, and a completely separate volume knob for the right channel.