The smaller the spindle, the finer the yarn I can spin, so what I've been spinning on my tiny Pax spindle is so fine that it could be used as sewing thread. In fact I showed it my friend D who teaches embroidery. She oohed at it's possible use as embroidery thread. The beauty of the 50/50 wool-silk blend is that it spins almost as easily as wool and shines nearly as brightly as silk.
As for me, my favourite use of fine yarn is for lace knitting or crochet. Lace is all about the spaces between the stitches. Of course the yarn and the shape of the stitches is what defines those spaces.
This pic is of a little insect who got caught in the house. I've never looked at a wing in so much detail before . . . and it's strong enough to fly with. I snapped this for a pattern before letting the insect go in the garden.
Of course the insect wing is stiff and I usually want a lovely drape in my lace knitting, though crochet lace is traditionally stiffened in some applications--not that I plan to be limited by traditions!