Material that is not safe for home is serious business. Typically, the solution for seeing material that is NSFW is to wait until one gets home, and then harness the privacy of one's own dwelling to safely access said material. However, there exists a category of material that is indeed NSFH. Not only can you not access this material at work without enormous risks, accessing it at home can be just as devastating.
Much of the NSFH designation depends on the state of significant others, parents, and siblings in one's life. Material that is labeled NSFH is material for which even the privacy of 'being at home' is insufficient. The risk of have a loved one discover a browser cache, site history, or random download remnant is too great. Therefore even greater discretion than normal must be taken to access this material in a safe way.
There has been recent outcry that devices such as the 'iPhone' will make NSFH a moot distinction, but even if the specific domestic risk isn't present, the NSFH license provides a nice indication when one is about to access material far less safe than one might have imagined, and will therefore be around well after emerging technology has made this particular distinction 'obsolete.'
Also, think about the FBI. Just think about 'em.