Why is this an issue?

Putting multiple statements on a single line lowers the code readability and makes debugging the code more complex.

if (someCondition) { doSomething(); } // Noncompliant

doSomething(); doSomethingElse(); // Noncompliant

Write one statement per line to improve readability.

if (someCondition) {
  doSomething();
}

doSomething();
doSomethingElse();

Exceptions

The rule ignores anonymous functions containing a single statement.

$max_comparator = function ($v) { return $v > 2; };           // Compliant by exception
$max_comparator = function ($v) { echo $v; return $v > 2; };  // Noncompliant