"It has its pros in so far as they rinse out very easily
Regarding soap flakes and one is not sticking one's oars into someone's wash water, but...
Just because forth vanishes at once when using soap at the first rinse that does not always mean the suff is gone.
What happens is simply fresh water with it's new mineral content causes the froth to go as the "cleaning" power of soap is now gone. Of course if one was washing you'd add more soap to compensate for this to bring the cleaning power back up.
A true test of if soap is totally rinsed from fabrics is if the water no longer appears milky, but clear. Even then soap never totally rinses free of fabrics and always leaves a slight residue, this is why items washed with pure soaps tend to feel softer and fluffier than detergents.
A small amount of vinegar added to the final cold rinse after several hot or warm ones will help remove the remaining calicum and other minerals from soap trapped in fabric. If done too soon however the acid in vinegar will combine with the fatty acids in soap and form a residue that will turn rancid and cause laundry to develop a whiff.
French housewives/laundresses had another age old method to "strip" soap residue from textiles and leave them whiter. They boiled items with one or more cut up lemons, then rinsed well.