The Free On-line Dictionary of Computing (30 December 2018):
A function argument which is used exactly once by the
If the argument is used at most once then it is safe to
inline the function and replace the single occurrence of the
formal parameter with the actual argument expression. If the
argument was used more than once this transformation would
duplicate the argument expression, causing it to be evaluated
more than once.
If the argument is sure to be used at least once then it is
safe to evaluate it in advance (see strictness analysis)
whereas if the argument was not used then this would waste
work and might prevent the program from terminating.