Michigan under Borges helm has not shied away from stack or bunch formations. While they don't run them as often as I would like them to be run, they are quite prevalent within the offense. Against MSU's press coverage it makes sense to run them more. Why you may ask.
Well here's MSU's coverage normally.
What this allows is for the Michigan receivers to get off the line cleanly and into their routes. More than that, it forces MSU's DBs to pick up the receivers after they have gotten into their routes, which is necessarily an awful position to be in, but it does make it more difficult for them to dictate and control where the receiver can run.
From this they can run a variety of concepts to isolate themselves on certain receivers. With protection, this gives Gardner time to make a relatively easy read: throw to the receiver that doesn't get help. This is a key way that Michigan can stretch the field or run triangle concepts to pick on the LBs underneath or isolated DBs over the top.
Like all things there is downside here though. This, for the most part, completely negates any WR screen ability. Bubbles are nearly impossible (they are very difficult against a standard alignment) because you can't get outside leverage on the block. Throw backs are difficult because the aiming points and runs are directly in front of the DBs (the only advantage here is that you already have them off the LOS). With the stack, you are also really losing the ability to attack outside in that direction because you have no way of protecting the alley. Any sort of even off tackle run is easily threatened off the edge because the crack block is difficult to reach. Which brings up the last point: MSU can blitz DBs from this because it's difficult to get into routes quickly with enough separation to run good, quick, hot routes. So when these are run, they must be run with care.