I have got a 12" delta that sees a lot of use. The large table makes it easier for me to sand curved pieces than on the belt sander with a much smaller table. I would love to have an edge sander too, but the disk sander with its downward stroke pushes the piece into the table instead of off the end of the table. If I was not a wood turner, and if I did more case work that was square, I would not find it quite as useful I do not thing. I also spent 4 years working in a boat shop where NOTHING was square. The 20" disk sander we had was invaluable. All that said, for some, a disk sander is just a really heavy paper weight.
Man advances just in proportion that he mingles thought with his labor. - Ingersoll