Chromatic has already commented on the (lack of) performance differences.

Obfuscation is in the eye of the observer (obfuscatee?), however. For someone who many years ago programmed in apl, so what? I believe that used appropriately, the trinary operation can be much clearer. For example, consider the following:

$some_variable = (defined $parm1) ? $parm1 : $default;
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compared to:

if (defined $parm1) {
    $some_variable = $parm1;
}
else {
    $some_variable = $default;
}
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and imagined it is duplicated 10 or 20 times. If you understand the perl syntax, there is no obfuscation.