I would never say that the general best practice is to reuse an object rather than create a new one. The best practice may be entirely the opposite. In the general case, NOT tinkering with an object's guts is the best practice. In the specific case where time efficiency trumps all other concerns, and the object is cheaper to reuse than to regenerate, then it may be a useful practice. That's about the strongest assertion you could make.
If it is useful in your case to reuse an object, it may be a good practice to create a subclass of the object that provides a "reset" method, or that allows "new" to be called on the object, with "reset" semantics, although that might confuse people who expect $obj->new to create a clone. The point being, such a subclass would allow the calling code to avoid touching the object's internals, which is a better practice.