This depends on which chemical you are referring to because different chemicals are beneficial in there own ways.
yes some chemical reactions are harmful to us. as digestion of food, photosynthesis, decomposition of organic waste are some examples of the useful chemical reactions.
water
kid
making cake
For each useful and expensive chemical a specific method exist.
Chemical stains make light microscopes more useful by showing specific structures in a cell.
So they can see if you are missing a chemical and to see if you are retainingthe chemical in your body.
energy
Chemical energy becomes useful to you when it is converted into a form of energy that your body can use, such as through the process of cellular respiration. This energy is then used to fuel various functions in your body, such as movement, digestion, and brain function.
chemical potential energy
Please provide supplier list of inhabiter chemical in mumbai only.
You think probable to catalysts, but they are useful.