Can NHD files be Safely Deleted from Save Folder?

I only really play one game (not counting test games that aren't intended to last long). It's multi-generational, I play many households in roation, and it's currently carrying 15 worlds courtesy of the NRaas Traveler mod -- the largest single nhd file is 305 MB. So the short answer to your question is that my sims and I are downright addicted to traveling. :)