Nature frequently freshens fresh water with rain, snow melt etc. Within the confined glass box of an aquarium, the only fresh water comes from the routine partial water change. Plants and beneficial bacteria can only do so much to purify the water. Hobbyists that think they can get away with few(er) partial water changes are only having their fish live in more polluted water longer....which very likely threatens their health and shortens their life span.
'The solution to pollution is dilution' and the very best medicine in the FRESH water tank is FRESH water.
Now having written the above, I believe there is such a thing as too much is a bad thing. In overstocked or neglected tanks, a large water change(s) can create a shock to the fish. I tend to do 25-50% every week without fail. Fry and grow out tanks will see similar volume water changes even more often.