the snow biome's version of silt
Fed into an Extractinator or a Chlorophyte Extractinator this pays out ores, gems and coins the same way Silt does, with the Amber Mosquito sitting at the far end of the odds as the reason people grind stacks of it. Any tunnel through the snow is worth mining out for it, since a stack costs you no more effort than the stone you are already throwing away and pays back considerably better.
harvesting it without taking damage
It falls, so use that. Dig out the block underneath it, drop a torch or a length of minecart track into the gap so the column has nothing solid to rest on, then knock the support away and let the whole thing collapse into item form. Standing under a pile while it comes down is how new players lose a lot of health to a block.
the spreads cannot touch it
Corruption, crimson and hallow all fail to convert it, which makes it one of the few things in the world that will never change color on you. Gravity keeps it from being a good quarantine barrier, though, so use it for the extractinator and leave the walling off to stone.