Sentence:  Thus optimizing the pipe as a component, and for just one benefit (saved pumping energy), "<WSD>pessimizes</WSD>" the system! Optimizing the whole system together, and for two benefits (saving energy and capital), yields fat pipes, tiny pumping equipment, slightly lower total capital cost, and 12 times less pumping energy. 
Meaning of the word marked with <WSD> tags:  To make (something) pessimal or the worst;  to make (something, such as a computer program) less efficient.