No difference really, they only hold slightly less. According to this chart, about 1/3rd less compared to 00 in terms of weight. So the only difference would be you'd have to use 1/3rd more capsules than others using 00 size ones.
So the benefit to use bigger capsules, means less work in filling and planting them.
So convenience then. Some sort of irony. When I was on here a million years ago, I pondered the use of garden fertilizers. Most everyone was like, DON'T DO THAT!!! Now it seems to be the thing. I still have my stash of Greg Watson.
Hmmm; there is a health food store that I used to visit for bulk seasonings. They used to have a bin of gel caps there. Wonder if they still do, and what size.
Pro-tip I picked up from Mr.Barr. You can use water as your "capsule" and just make ice cubes, that way you can make them any size/shape you want. You have to not fiddle around when planting, but they don't melt too fast. He also does this with just soil and water, instead of osmocote or similar things. But that can be a little messy if your not quick ime.
Edit: Hmm, just thought of a "improvement" on the mud cubes. Would require a little more work but, no mess. You could "double freeze" them, in like you make a mud-ball/cube freeze it, take it out. Put it in another/bigger tray and just add water and re-freeze. That way you should get a time-buffer of just ice/water melting before it gets to the mud. Also seen some people on you-tube just use gelatin (same stuff capsules are made of, can be found cheap in jelly-making isle in stores) and ice-cube trays.