While there are many who want their base to be as pure as possible, I find my 40-50ppm water to do very nicely. The threshold is debatable, but under 150ppm should be considered just fine for many. Others not so much.
As far as growth, low very ppm vs. moderate ppm, can't imagine there'd be a difference.
When you need 5+ gallons, tap becomes very convenient, especially if you grab a 5 gallon jug initially from a store. If your source uses chlorine and NOT cloramine, you can simply fill a jug and leave uncapped for a couple days, chlorine evaporates fairly quickly. Those are the pros for me.