I live in an area with some of the hardest water in the country and the technician that fitted the machine a year ago advised that in my area I should always use salt and rinse aid, even though I use the 3 in 1 tablets and, to be honest, I do notice the difference.
I can get down to the salt container but I find pouring the salt into the container is a real b****r. Although the manufacturer supplies a funnel to pour the salt in , the slightest knock sends it flying and the salt usually comes in plastic bags, so the flow is difficult to control and I seem to get as much salt in the base of the washing machine as I do into the salt holder.