I don't build, but when I had a bass built I asked for an asymmetrical neck.
The benefit to me as a player is that it made it easier to navigate a fairly wide neck. The neck being thinner on the treble side means that there is less 'meat' to have to reach around when I'm playing on the E and B strings. As my fingers get lower to access the D and G strings, my hand rotates around a bit and the thicker upper part of the neck kinda fills my hand up comfortably. On the A string, it splits the difference.
It's not a huge difference from a standard neck, but it's noticeable and I find it very comfortable to play on. I had previously owned a Tobias bass with an asymmetrical neck and that's how I became familiar with them.