There are conflicting opinions on the harms and benefits of oversizing systems. There are many reasons why around half of the responders continue to oversize despite the energy concerns and the most popular reason is to make up for variations during system operations, while some other reasons were based on taking preventative measures.
Many feels that it is better to be safe than sorry and others think that the price of an oversizing system is easier to handle than the price of an operational mishap. Knowing your system is the best way to avoid the need to oversize, whereas studying and understanding process needs narrows the margin for errors.