Ok, but why the baking soda?
In Beersmith, I used the Water Profile tool and clicked the "Calculate Best Additions" button. That combination of additions is what it gave me to turn 5.25 gallons of RO water into Mosher's ideal pale ale water profile.
What's the mash pH?
I don't yet have a pH meter, so I used the EZ Water Calculator spreadsheet, which estimated the room temperature mash to be 5.41. A pH meter is on my list of equipment to buy.
I probably put too much trust in Mosher's ideal pale ale water profile, that that combination if ions in the water would be good enough to not cause a bad taste nor a bad mash pH. As well, perhaps too much trust in a spreadsheet rather than a pH meter.
In any case, I think water preferences are a matter of taste, just as hop flavor is so I don't think either is "bad" but I don't add unnecessary salts and I make sure my mash pH is optimal, and that's about it.
I'm still learning, and still buying equipment; I've only been brewing since November. The water report for my village's wells show it to be extremely hard, which is why I've been experimenting with building water profiles from RO water, which I can get cheap locally.
Some day, someone will produce RO addition recipes for mash water and sparge water based on beer style.
Thanks for all the feedback. It really does help people like me who are trying to absorb it all.