There's a few reasons why I put the effort into mulching those potatoes.
...weed control. With all the moisture plus not being able to repeatedly walk through the crop to scuffle hoe, the weeds have been having a party. I see certain weeds returning to the garden beds because of my heavy use of homemade compost and mulch. This is to be expected and normally isn't an issue. But this time around, the weeds haven't been smothered with mulch. Thus the weed seed has been germinating out of control. So what have I done? Did I need to pull or chop weeds prior to applying mulch? No. I simply covered the weeds with the grass clippings. And if Mother Nature allows, I'll apply another layer of mulch in 2 weeks, just about the time some weeds will be poking through this first layer of clippings. So the weeds aren't an issue for me. No need to put the effort into pulling weeds.
Above, lots of weeds between the potato plant.
...prevent greening of the taters. Ever wonder why the garden books recommend hilling your potatoes? Hilling refers to pulling the soil from between the rows and depositing it around the base of the potato plant. No, it doesn't mean making a mound and then planting your seed potato on the top of that mound. Potatoes aren't meant to be planted atop a mound. Hilling accomplishes a few things. It destroys the young weeds in the aisleway, smothers the weeds around the plants, plus builds a barrier against the light for the developing tubers. My mulching does essentially the same. By blocking the light, the tubers won't get green where they are exposed. Green tubers aren't good.
Under more normal weather patterns, mulching would also help keep the soil moisture fairly constant. That's important for tuber development. Fluctuating soil moisture can result in tuber deformities....splitting, knobbing, hollow hearts.