Well I use it because I actually like the softness and slight scent it gives, but it seems I'm in the minority here! I don't use a lot (maybe a tablespoon) and clean my dispensing drawer once a month. Our water here in Herts is appallingly hard and if I don't use it the clothes feel like cardboard. I've tried the white vinegar tip, but it made no difference at all.
I also use professional cleaning crystals in the washing machine and dishwasher every couple of months (they were recommended by an old-time washing machine repair man) and in 44 years we have had two dishwashers and three washing machines - not bad going, I think!