so why exactly is everyone using the kreg instead of good old dato's. Are the Kreg joints better,stronger or is it a time saving thing?
The joint you are referring to is a dado joint. The reason for using pocket holes instead of planing, sawing and chiseling or routing out a dado is because it is quicker and easier. My guess is that pocket hole joints were invented by a furniture manufacturer sometime in the last century, since you see a lot of factory made furniture with pocket hole joints. But dados are still cool. Now a dado joint reinforced with pocket hole screws -- that would be a really strong joint! You would subtract the dado depth from the spacer height for the thickness of the being drilled. I don't remember the height of spacers, but you could make the dado depth in spacer increments (one or two at the most) and subtract the requisite number of spacers from the jig.
If you are building a box or a shelving unit with fixed shelves, there is no need to used edge trim to cover the end of the dado or the need to go through the effort to make a stopped dado.