There's a lot of discussion in Leather as to whether the submissive should walk/stand on the left or the right of the dominant. I don't really know if I believe in one true way for this, I think whatever works for people is fine. But anyway, that's not what this is about.
I often prefer to have my submissive on my left side. It just feels more natural, or better, or something, I don't know. I just know it's what I prefer.
Today I had a lightbulb moment which explained why!
At karate (which as I'm sure you all remember, is practically my base for my life in Leather) we were lined up in a very specific order. Sensei at the front of the class, of course, and then we were lined up grade by grade, from left to right. Those who were of a lower grade than you, were always on your left.
So in my formative adolescent years, I had already learned that those lower than you in the chain were on your left, and those higher on your right. It's unsurprising that that subconsciously stuck around even long after I had to leave karate! :)