Side reactions are undesirable for several reasons. Firstly, they can reduce the yield of the desired product, making the process less efficient. Secondly, they can create impurities that complicate downstream processing and purification. Thirdly, side reactions can lead to the formation of hazardous by-products, posing safety and environmental risks. Finally, they can increase the overall cost of the process due to the need for additional steps to remove or neutralize unwanted products.