The reasons why I tune my instruments a little lower than the accepted standard is that I love how it sounds and how it makes me feel. Over the internet there are numerous discussions about changing the A4 which is the reference tuning note from 440Hz to 432Hz. It is only 8Hz and only people with trained ears would tell, but there have been experiments in which the subjects had to listen to the same piece of music in both versions and the majority preferred the one tuned to 432Hz.
Considering that music is not about arcane calculations or possessing a special ear but feelings, feelings, and more feelings, I still see lowering the standard tuning as a very valuable proposition. As I have been using it for more than ten years, I would like to share my humble experiences.
First of all, for me, it is a necessity as my inner ear's pitch was created when, as a child, I would listen to my parent's collection of LPs through a slightly out-of-tune record player. In my late teenage years, I even disassembled it and re-tightened the belt to spin faster to catch up with 440Hz. But at that point, my musical memory was formed, and forever after, when tuning a guitar by ear with no reference pitch, I was always slightly flat.
Second, Django Reinhardt, Jimi Hendrix, and a few other blues players often tuned to a pitch within 0.5 to 1Hz plus or minus the A4 at 432Hz. And for me, that should be enough to say that if it sounded good to them, it certainly should sound good to us mortals, as they knew a thing or two more than us about beauty, feeling, and groove.
Third, since my early experiments with it, I have noticed that audiences tend to hang around longer during a music performance. Also, when playing in an open space with no seats, they even come closer and closer to the stage as time progresses. Besides, the musicians in the band are more relaxed and less in competition with each other.
Fourth, it really sounds good! At A4=440Hz, the acoustic guitars (classical, gypsy jazz, archtop, etc.) have three contrasting tones: Bass, Middle, and Treble ranges. It's like playing three different instruments. It is a pain to deal with and probably the cause of infinite buying and selling of musical instruments in search of the elusive Holy Grail. At A4=432Hz instead, the guitar sounds warm and coherent from the lowest to the highest note, and we can finally relax just thinking about the music that wants to come out of our fingers.
I haven't gone into any technical explanations because, as I said, music should be about feelings and not theory. But if you have any questions or experiences to share, I would love to know what you think.