Opacity vs Alpha and then there is Opaque


First part of the question, What is the difference between Setting opacity to 0% and setting Alpha to 0. My 3D experience tells me that alpha is the transparency of the object.

Second part, while doing my own searches about the above question I have come across many instances of advice stating that if our views are every transparent that it is useful to make Opaque FALSE which would allow some optimizations to happen. Furthermore, I have found advice stating that having something with an alpha of 0.0 and having it opaque could cause unpredictable operation.

Any help would be much appreciated.

On a side note, this is been hands down the best programming book I have read in a very long time.