Due to extreme laziness I gave up earthing mine up years ago and I can't really tell the difference in yield.I messed up with mine....didn't earth them and now I have 4 foot high potatoes. I suspect it's not going to be a good year for spuds!
I plant my spuds with a dibber (poke a hole as deep as I can and drop the seed potato in, then cover it over) and they always do OK. If the yield is a bit lower, plant a couple more.

I was told that earthing up is more to stop late frosts damaging the emerging plants than anything else, (but that could be rubbish).