Where the shoes bolt onto the chains, there are already small holes in the shoes. These holes let a small amount of material pass through each time a sprocket tooth enters the chain. They aren't big enough to allow a lot material to pass through, though. If one large hole is drilled on center with the link, it will allow snow and mud to get pushed through. This will prevent the links from getting packed with ice which will cause excess tension on the tracks and could make the sprockets jump (it makes a sickening sound when it happens
)
The down side to the enlarged relief holes is that it's an access point for more dirt, sand etc to enter your tracks.
I can't see that relief holes on the shoes will make much of a difference for keeping the tracks clean in general. You still have to shovel out your tracks at the end of the shift.
Last time I had to track through snow was last winter in Iceland. There was 3 inches of ice on the road so the lowboy couldn't come and get me. The PC300 was up in a snow filled quarry in the hills. I took it for a 3 hr walk through the snow. The found that the best thing to clean the snow out of the tracks was when I took it through a 2 foot deep river that was frozen ontop but moving pretty swiftly under the 5 inches of ice. (Crossing and tracking down the river cut a half mile off my trip).