This isn't a topic where you can run on the anecdotes of others unless you have the same water from their same tap. Even if you find ten thousand people who are running fine on their tap water, it doesn't mean squat about how it will work for you.
It's like asking if you can get away without having flood insurance. It depends entirely on where you live. I'm fine, the river would have to be up by 100ft or more to flood my house. Ain't never gonna happen. But my friend that lives down by the river would do well not to think he can eschew flood insurance just because I've never needed it.
There's one in every group.
What do you mean? There's at least one person in every group who is at least honest about the uselessness of the information that comes from a question like this? There's at least one person on every group that has some sense?
Do you really think that the results someone has with their tap water two states away from you has any bearing on how well your water will do? Do you really believe all tap water is the same?
^^^What he said^^^
Unless you can compare tanks from the exact same source water, one using tap and one using ro/di, there really isn't anything meaningful to be learned.
My experience is as follows:
For ~22 years, I used Columbus, Ohio tap water with no conditioner of any sort. I would fill my mixing barrel after water changes and then it would sit and naturally off-gas the chlorine in the water until the next top-off, usually a couple days later. 2 days before water changes, I would top off the barrel and get salt mixing (IO, IORC, whatever was on sale).
I never had any problems that I could attribute to the tap water, but there were certainly seasonal problems with algae, nitrates and phosphates.
About 8 years ago, I decided, after reading here and elsewhere of the benefits, to make the switch to ro/di. Part of that was the desire to keep more demanding corals, part of that was - well - just because everybody else was.
I haven't looked back once or regretted that decision in the least. My nuisance algae/nitrate/phosphate issues went away. Turns out the likely culprit was runoff after summer storms being passed down the line. I can now keep pretty much any coral I want without much trouble. I even ran a line from the RO side up to my refrigerator for water and ice. No more $35 fridge filters!!!
That, however, was my experience. Yours may very well be different if you have a different water supplier.
hth