I've never really used "kevlar" thread myself - probably reflects the limited range of flies I tie.
I do have some of the finer GSP threads that seem to have superceded it to some extent. I don't use them much - far too slippery to tie with. Good for thread ribs ( as kind to trouts teeth as they are to scissor blades

), really heavy dubbing loops ( you can spin them forever without the thread snapping) and for binding down things that require a lot of pressure, maybe. Apparently they're also popular for heavy deer hair work with some experts.
For general tying I'd forget it.
And Kevlar could do serious damage to your tiny little hands, Fred

.
.D.