I have stitched on leather, suede, card stock and paper, along with all sorts of fabric with really good results. I have seen others that have stitched on ballsa wood, shower curtains, golf bags, canvas bags & suitcases, burlap, sack cloth, vinyl, fleece, fur, chamios, suede, mylar and wool.

I think it is all in what you are willing to use on your machine. And of course, what your machine is able to go through.

I sometimes will handloom some rugs using cotton fabric strips, then I will do some embroidery on them. I did a kitchen rug with those picnic ants on them, it got snatched up at the first show I had it in......Also will sometimes embroider on my handknit items or felted purses...

I have stitched on paper, card-stock, leather, suede, vinyl and all sorts of cloth - linen, cotton, fleece, knits including hand knitted items. And I put initials on rucksacks and totes without problems. I have not tried balsa wood but I have seen beautiful examples in Projects - a.o. the rose I digitised for card-stock, I was amazed!
Needles used for card-stock I keep separate as it dulls the point more than cloth.
It does not seem to have a detrimental effect on my machine, my Designer1 is almost 12 years old and in good working order.