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You put the softener at the inlet to the house because you don't want to have hard water flowing through the pipes in your house. Hard water precipitates minerals that ruin the piping, hence you put the softener at the main inlet.

The softened water is for more than just comfort of use though. It keeps the hard water from depositing in the pipes and any of the devices that have water pass through them. It was interesting when we installed a better softening system that our water heater started putting out hotter water since the elements got cleared of the deposits. It also stopped making creepy sounds.

From what I've gathered, hard water also lowers the life expectancy of the RO system.. Also you may want softer water for cleaning dishes, since softer water means better lather with less soap, saving your detergent.