As A hobbyist, I have a 6" Jet jointer bought in the late 90's. Like Jim, mine does not change adjustment, unless I've changed knives. It takes roughly 64th off each pass.
I've done some pretty big work with that jointer, but make no mistake, it is woefully too small. I use a carrier sled with my 15" planer a lot!! Just about every project has me making, or retrofitting, some type of a carrier board to compensate for the jointer being to small.
Minimum size in a hobbyist shop would be 12" wide for my needs. I am constantly jointing and planing boards wider than 8". I do not believe that helical cutter heads are a necessity, but boy they sure are nice, but so is a 27" dual drum sander.
To edge joint, or face joint, a 4' long board, a relatively short board, takes up 8' of linear space. Whether it's air space, or a jointer bed, doesn't make any difference. You just can't have a big enough jointer, or planer.
Someday, I'll refurbish and overhaul the 16" jointer I bought off Craigslist many years ago. I've fired it up a few times, playing around a little bit, but haven't really put in the work to make it usable. It's also a square cutter head, and it can take off material really fast. Those knives are a 3/8" thick. It's scary, but cool at the same time.
"The first thing you need to know, will likely be the last thing you learn." (Unknown)