pH is important because if it's out of range for the medium you're growing in, certain nutrients can't be uptaken, which causes an artificial deficiency situation. Plants can't grow and develop properly without access to all 17 elements and nutrients they need.
Be cautious about how you manage pH long term:
Using vinegar for pH down isn't really efficient. You have to use so much of it for such a temporary fix, that extended use will kill or at least harm the plants. pH Down, citric acid, Sulfuric acid, Phosphoric acid are a few alternatives.
Using Sodium Bicarbonate (Baking Soda) as a pH up for extended periods can lead to salt buildup in the medium, again possibly causing artificial deficiencies and lockout. pH Up, Calcium Hydroxide, Potassium Hydroxide etc are some others.