It is imprudent to assume that the utility (use or uses) of an invention would be obvious to the reader. For this reason, the disclosure should state specific, credible use or uses of the invention and explain why the invention is useful to clearly establish its utility. The use or uses must be credible to a person skilled in the art of the invention.
Hint! After you write your statement of utility, test it by asking yourself whether the rest of the disclosure supports your assertion. Remember that only one of the asserted utilities need be credible--so state all the "uses" of the invention that you can think of. The use that is "credible" need not be the most important or most valuable use of the invention.
Law - Utility of the Invention