I did the last time and it was amazing. If you are going low and slow you will never render all the fat. Just left a meatier, more delicious final product. Better bark, too. Quick YouTube search shows a lot of guys recommend it.
How much trimming do you do to the belly before cubing up? My family is noses up to any non-rendered fat. I think if I do these again, I will remove the entire fat cap and trim a bunch of the hard fat off the top, as well. I did minimal trimming, but left about a 1/4 inch on the cap. I gotta say, I went a bit crazy with the trimming on the last pork butt that I did and it turned out better than any I have ever made.
I haven't prepared a pork belly as poor man's burnt ends yet. I've only done chuck roasts and there isn't much to trim off those.
As far as a pork roast on the smoker, I trim some of the fat off, down to about 1/4" or so, and let the rest render. My wife doesn't much care for any remaining fat, either, so I make it easy on her...and myself.