Do you use parchment paper when baking meat in the oven?

If you cook bacon or fish on a sheet pan in the oven, do you use parchment paper or lay the meat directly on the pan?

As an anecdote and follow up question: at one restaurant I worked in, we would par cook bacon on a sheet pan using parchment paper with a grate over it, so the bacon wasn't directly on the paper. At my current job, we lay the bacon directly onto the parchment without a grate and the topside cooks, while the underside remains pretty much raw. My guess is that the paper is insulating the bacon from the heat (whereas laying it on a grate allows air circulation under the bacon, so it cooks evenly). Is that right? If not, what's the difference between the two methods?