Oil is heated primarily by rpm's. If you're road racing and ppushing the rpm's hard, the
oil will get hot enough to be a small problem. On the street, drag strip, and autocross course, the
oil generally stays within 10-15* of the water temp.
The bottom line is, unless you're road racing, skip the cooler. It will only add weight, complexity, cost, and failure points.
Some people like to install the cooler in the lower opening just for looks. If that's the case, don't connect the lines to the engine.