I brewed for about a year (50 batches or so) with straight up Portland, OR city water, which is very soft and has a ph of about 7.5. This seemed to work fine for me except that theoretically the hops would pop more with a higher amount of sulfates, and for darker beers the mash is too acidic. These problems were hard for me to notice, but I suspect they were there to some level. I made mostly beers under 15 SRM, so the mash problems were probably muted.
About 10 beers ago I switched to adjusting my water. Depending on the recipe I have used gypsum, chalk, calcium chloride, baking soda, and epsom salts. I used the ez water spreadsheet and watched Bobby_M's videos which were very helpful.
I can't tell you that it makes a huge difference for me to make all these adjustments, I haven't done a side-by-side with the same beer yet, which I can do in about a week with a porter that will be ready.
The thing that is nice about having clean/soft water is that you can build it up very easily and you will never have to cut it with other water, and it is likely that it will work "ok" for you unmodified as it did for me for quite awhile.
Here is the detailed profile of my water, kcinpdx posted this in another thread:
Primary Contaminant
Fluoride (F) <MRL
Secondary Contaminants
Chloride (Cl) 1.9
Fluoride (F) <MRL
Hardness (as CaCO3) 5.1
Sulfate (SO4) <MRL 3.7
Unregulated Contaminants
Alkalinity (as CaCO3) 8.5
Hydroxide (as CaCO3) <MRL
Carbonate (as CaCO3) <MRL
Bicarbonate (as CaCO3) 8.5
Carbon Dioxide, Free (CO2) 1.1
Carbon Dioxide, Total (CO2) 8.5
Calcium (Ca) 1.1
Cyanide (CN) 0.046
Magnesium (Mg) 0.6
Potassium (K) 0.2
Sodium (Na) 2.6