If a local variable is declared but not used, it is dead code and should be removed. Doing so will improve maintainability because developers will not wonder what the variable is used for.

Noncompliant Code Example

function numberOfMinutes($hours) {
  $seconds = 0;   // seconds is never used
  return hours * 60;
}

Compliant Solution

function numberOfMinutes($hours) {
  return hours * 60;
}