It's not a waste of time. Check these links from something I posted recently:
And water adjustments do not need to be complicated. For RO/distilled/'low mineral' water, take a look at Water Chemistry – How to Build Your Water – Bertus Brewery
Yes, maybe. It depends on your water source and time of year. It also depends on your taste. If you build your water from distilled or RO water and you like the beer better, you didn't waste your time. If you don't notice any difference then maybe.