Tracked excavator slip-on transport dollies - GIF

[KustomsbyKent]

I believe it is to minimize wear to the undercarriage system for the tracks. Roller and track plates and sprockets have wear happening during movement, so minimizing movement decreases that wear and so saves significant cost. Pricing undercarriage parts for even a small excavator are expensive....so I think its a safe assumption that these big ones are proportionally expensive!