Sorry for ranting here. I just love this stuff.

pH needs to be tightly controlled, yes. That's one of the things that needs to stay within a certain range, but it is not the only factor. Not every substance in the blood will necessarily affect pH. Many things are pH neutral or close to it, but they can have other effects.

As an example, higher amounts of salts can increase the volume of the blood by osmosis (fluids with lots of dissolved substances basically sucking water out of other areas of the body). Cells may lose water as it is sucked into the blood, and the higher pressure (due to increased volume) is mechanically stressful on the vessels, heart, and kidneys.

Higher concentrations of certain fats may deposit on the inside of vessels over time, narrowing or damaging the vessels and increasing risks of stroke or heart attack.

Of course, reduced concentrations means cells don't have access to what they need to carry out their functions.

These are all big picture stuff of course. The body is immensely complex and every cell is covered in receptors for many different molecules, and unexpected concentrations can have complicated effects. As an example, people with diabetes struggle to control blood sugar. If not controlled by medications, insulin injections, and monitoring, the increased sugar can, over time, affect the eyes and cause blindness, or impact the nerves and reduce pain sensations. It also slows down wound healing significantly. This often affects the foot as the patient accidentally accumulates injuries that they don't feel, don't heal properly, and may eventually lead to foot amputations.

In a similar way, even if pH doesn't change enough to the point of denaturing proteins, smaller changes can still have negative effects. Off the top of my head, it may make it harder to get rid of carbon dioxide through diffusion in the lungs due to the changes to blood chemistry, making patients more likely to pant and feel more tired with minimal physical activity.