If you have a game that allows players to save their progress on their own computer, it may find it useful to secure your game's savefiles from modification so that people can not cheat quite so easily. It should be noted, however, that this does not in any way prevent players from examining their savefiles to see how they work, it only protects them from being modified.
Using this library is easy. Once installed, all you have to do is run your savefiles through safe_save() to create a new, secured version of your savefile. When you are ready to load the savefile again, use safe_load() to verify that the savefile has not been modified. It will return your loaded savefile if everything is well and good, but will only return null if the file has been altered.
This method is not 100% full proof, since there are ways to bypass it. However, as the hub page points out, it can not be "trivially circumvented", so it should be enough to keep the vast majority of your players from cheating.
For further instructions on how to use this library, download it and look at the demo source and readme files.