@ceilingcat - The kidneys are a very important organ. I think they're kind of underrated, but basically their whole job is to filter waste out of the body. If they don't do that, you will die.
Anyway, it sounds like this little group of cells has their work cut out for them. Processing all of the fluid in the human body 15 times a day sounds like a lot of work. I imagine it would be very detrimental if the macula densa shut down or were damaged somehow.