The idea was to carry several small zip-ties with you, and use those to secure the zippers on luggage to make them more difficult for a thief to open. Nail clippers were the perfect tool to remove the zip ties when you were ready. I know that TSA regs have changed what you can and can't lock in checked and carry on bags, but IMO this remains a good way to secure items that you don't want people to be able to easily open.
I fly a lot for work and this is exactly what I do with my checked luggage. All the zippers are ziptied shut and I carry a toenail clipper in my travel vest to cut the zipties when I arrive. I've never had the TSA or its equivelent in other countries question this process, cut the zipties or try to confiscate the clippers. Nor have I ever had anything stolen from my bags.
-Blast