Certain purveyors of half truths have led me to believe that the "? :" syntax and the "if then else" syntax spring from the same goodly source.

Equivalent uses of them likely produce identical opnodes for Perl to execute. But "if" is meant for use on statements (or blocks of statements). "? :" is meant for use on expressions. The precedence table (for Perl and C and many other similar languages) treat assignment as more like a statement, not just an expression. So, to include an assignment inside of an expression, you usually need to enclose that assignment inside parens.

This can be a good reason to adopt a style that avoids using "? :" to pick between different assignments. On the flip side, I have had people argue that code like:

if( condition() ) {
    $a = one();
} else {
    $a = two();
}
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is better written, style-wise, like:

$a = condition() ? one() : two();
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Which I can agree with in some cases more than others.