pH is important and a vital element to succeed in growing plants. An imbalanced pH leads to unhealthy and in extreme cases, failure of crops. 

Why is pH important to crops? Plants absorb major and micronutrients at a certain pH range. This range varies from crop to crop. In vegetation, if pH is imbalanced, it causes nutrient deficiencies either in major nutrients or in micronutrients. 

Symptoms of nutrient deficiencies start with the yellowing of the leaves and if overlooked, can lead to the demise of plants. In hydroponics, plants are more sensitive to excesses and deficiencies from nutrients as the roots are soaked in the solution at all times.
 
Thus it is very important to manage the chemistry of your water by ensuring the correct pH. Soil vegetation on the other hand is forgiving as the roots are not soaked and the medium in which the plants grow becomes buffers.

HYDROPONIC TIP: In hydroponics, you should have a pH meter. Not having one means you are guessing all the time. Get your pH right from day one and you will harvest the biggest possible yield at the shortest possible time.