I had a validation method like:
$valid_types = array(0,1,2,3,4);
$type = 'string string string';
var_dump(in_array($type, $valid_types, true));
Without executing it, what do you think happens?
I thought: bool(false), bool(false).
WRONG! in_array() does type conversion, so (int)"string string string" is 0; and yes, that's in our array.
So; to avoid surprises, always supply the strict param to in_array().
Its also a good thing to keep an eye on with code review.