Water Chemistry & Beersmith

Im just getting started on this topic, and already Im a tad confused as to why you would want to conform to a particular regions water.

Wouldn't most of the breweries around the world be adding salts and buffers to their water in the brewing process? Wouldnt this make the beersmith profiles  for example...effectively useless?

I could understand having a particular water profile for a style of beer, but surely a regions water measured on its way in is in no way indicative of the water that goes into the mash for that style of beer

I also have a few questions regarding the use of the 'EZ water calculator Spreatshet 3.0"

Here's what my initial calculations look like.... My starting water profile is spot on as I have a report from my local treatment facility. First off, does this look ok? a residual alkalinity of -49 should be ok for a pale ale ya? I added a few salts to try and bring it within this range.

Now.... I want to add this new profile into beer smith so it can pop the ingredients into my recipe...when I make two profiles in beer smith, one with my original profile and one for a target (which Im calling 'perfect water').... Why are the calculations so Different from the above? With these beer smith calculations I end up with a RA of -38 and my magnesium levels then drop below 10.

Is this the right way to go about changing your water makeup? Should I just be selecting a region in beer smith? Or am I on the right track trying to target the water to a specific beer with the spreadsheet and just add those salts..... Is there a good spreadsheet or thread detailing the water needed for certain styles of beer?

Also, what sort of acid should I use to knock my mash PH down a little more? If Im adding sulphuric for example, do I need to account for that by trying to lower my initial sulfate concentrations? Or would the small addition needed still leave the sulfate within the 50-350ppm range. What about the chloride/sulfate ratios?

Thanks for any advice and input..... Learning fast at the moment