the end results are the same

if ($3 == this) || ($3 == that)
means, if $3 is this, or if $3 is that

if ($3 == (this || that))
means, if $3 is this, or that

its compressing 2 'virtual' if's (since the second, in the first example is a 'virtual if') into the single if, it would however, give the same outcome.