Interestingly enough as normal as salt containers are in dishwashers as 'uncommon' are house wide water softeners to me.

I know a few people who have a single outlet for osmosis water, I use a optional water filter in the kitchen outlet for drinking water.

But nobody I know is softening their whole water supply. Why soften toilet water? Why soften cleaning water? Garden water?

Well for the last 2 I guess it depends on how hard it really is

Softening toilet water means there’s less limes SLE build up in the bowl and around the rim which means the toilet is easier to clean.

Softening cleaning water means your clothes come out - well, quite literally softer. And last longer.