Doesn't seem to work if you keep stock at zero and just check active. I have an item with 4 different unique SKU's. I set one of them to active, and it only makes active the parent SKU on the mass edit page. And then it's not really even active. You edit the product individually, and it hasn't changed anything.

This scenario comes up when you just when you want to prevent selling an item, but want to keep the product page there. Checking active with a stock level of zero is a good way to do this.