Before I started to use software (Bru'n Water for me) and a pH meter I could only make decent darker beers. Why? Because my water is unbelievably alkaline. Anything lighter or hoppy ended up either sweet, muddy, no crispness or just kind of "meh" for lack of a better term. Control of pH and use of CaSO4 and CaCl2 to adjust flavor made a world of difference. That, and switching to all RO water and back adding salts.
In addition, it is really fun to get some sort of BMC and dose samples of it with different amounts of CaCl2 and CaSO4. You can drastically change the flavor profile of a beer with just those two salt additions (or lack thereof). Find out the levels you like for different styles of beer. SO4 is important for IPA.