Valhalla,
Going out on a limb here, as in contrary to what you've been given for much of it.
I've had to rid myself of some really bad habits when I first began casting a decade ago. So I cast on my back yard lawn grass....nice, green "Barefoot" type grass and practice around 4 days out of every 6, for around an hour at a time.
Been doing this for over 3 and maybe 4 years now, religiously and have not hurt any of my SA GPX and XPS lines as yet.
I clean the lines with the SA cleaner EVERY time I go fishing and when they need it for back yard casting....which may be once every week.
No problems. YMMV....
Jeremy.