Return value efficiency question

Consider this method: function xyz() { return $this->data = unserialize($this->serial); } A few assumptions: - Resultant data large enough to warrant discussion of efficiency - I always want to store the unserialized data into the object - The return value is only needed sometimes If I only need to grab the return value on occassion, what is the overhead of returning the value, if it's discarded most of the time? Example: $obj->xyz(); // method returns data, but nothing is done with it Same difference? Or better to break this out and only use return when needed? Appreciate any expert responses. I don't know enough about the internals of PHP to know the implications of this... thank you! --Kelly