So far, I always cold crash to get the impurities/ carbohydrates to fall out of the solution and leave a less hazy wort. I like a gnarly trub in my kettle, before I start transferring to the ale pail/ bucket fermenter. So, I don't know what a beer would taste like without it. I've only brewed ales and lambics so far.
Not all tap water is good to drink. Some people wells or some city water is bad.
Personally I only buy it if the power is out (to help pack the fridge and freezer) or road trips / camping. Where yes is could try to store a coolers worth of ice in my freezer but its just not worth it