I can't imagine ever going back to a non-split keyboard; for me, it's a much better typing position to have my hands shoulder-width apart rather than squeezed together. I think that's more important than the "every key is within reach of the home row" argument for the 40% size in particular (although I've kind of fallen in love with the 40% size, but I could cope with going to a larger keyboard again better than I'd cope with going to a non-split, I think)
But more than that, as a programmer, there's something meditative about maintaining the custom hardware I use to do my job. Double-checking the soldering, tuning the firmware, taking it apart to polish the components and then putting it back together again, etc. Reminds me of the Zen of Motorcycle Maintenance, in a lot of ways.