I've been doing SUL trips, mostly solo overnights, for a few years now. I think I sewed my first (and only) SUL pack around 2006/2007...roughly when the BPL article "Five Yards to SUL" was published.
While not practical for all conditions all the time, my SUL kit has taught and enabled me to do a few things:
*I enjoy exercising minimalism. This is a theme in my artwork and life in general and I enjoy extending it to backpacking. Trying to minimize the amount of stuff carried by reducing everything to it's simplest form, discovering dual-uses for as many things as possible. I see it as a form of backpacking that is actually the opposite of the highly gear-centric attitudes we find here. My SUL kit is very simple and was very cheap to build; no cuben fiber or expensive products, much of it made myself.
*Getting a down to a sub-5 base has enabled me to do many hard solo runs and trips in the mountains with a measure of safety. Heading out for a solo 50K+ run was a little daunting at first- the idea of getting hurt and/or lost and being stuck fairly deep in the mountains alone and without gear is intimidating. But running with 5lbs (or less) of basic gear is not an issue and provides flexibility, as well as a big safety margin. I enjoy going on runs in which I can simply spend the night if I'm tired or continue on in a single push if I'm feeling good; all without the gear really getting in the way.
*SUL spills into other gear lists and gets me in the habit of really questioning function and design. I enjoy this in itself.
Good question Ron.