Good question and I'd be interested to see the responses. Years ago I bought some decal paper, I'll have to dig it out and see what brand, and used it once for the plaid seat inserts for the ZZ Top Ford.
The challenge I had is that at home I have inkjet printers. You have to spray the paper with flat or semi gloss clear, let dry, print the decal, let dry, then spray again with mist coats of clear. That stops the ink from running when you dip the paper in water to release the decal. That's quite a bit of work for someone like me with a short attention span.
Another problem I ran into with the inkjet is that printing small decals resulted in more dots than a clear image. I believe with a laser printer these are not an issue.