On a camaro forum that I visit, several folks have used those to clean/media blast the underside of their cars and they are handy. They make some welding positioners, but I feel like the time it takes to load and unload really defeats any advantage they may offer. Another thing is we have way too many work tables to buy one for every table.
The biggest obstacle when turning some pieces are the full pen outriggers. When you have to position the beam/column with the outrigger pointing down to the floor, if the outrigger is very long you have to jack the beam/column way up in the air and then climb a step ladder to weld out that turn of the piece.
Typically, we lay it all out on the "B" face(web near side) with soap stone and then transfer the fitter's marks over to the other faces as needed, then fit up one face, turn, fit up the next face, turn, so on...then after the fitup inspector has given his OK dimensionally, they weld out the face that is facing up, turn, weld up the next face, turn, so on....
a video showing all of this turning would be great!