The difference is the precedence, which can be handy not just for opening files. I still prefer to use parens when I open cause I like the look of it better, but then use an or as well.

You can also mix them to make some checks easier, seeing as || has a higher precedence than and, saving some parentheses.

if ($a || $b and $c)
if (($a or $b) and $c)
if(($a||$b)&&$c)
[download]

All of these lines are equal.
The parens add readability, but hey, maybe you like the visual of only one set of parens. :) TMTOWTDI

~Brian