I live in Chicago. That means that the weather usually sucks and people want to steal all of your things. I recently had my handlebars stolen off of my bike - and it was very clear that the person who did it wasn't very tool savvy. That said, if I had these little plugs installed at the time, they probably would've walked away defeated.
These little plugs are meant to do 3 things:
1) Make it slightly more difficult for someone to steal your parts in a pinch (they take a little work to pop out)
2) Prevent shitty weather from destroying your bolts over time. In Chicago, we get rain and snow like madness and the salt during the winter here is unbearable. My bike is filthy from November through May.
3) Give your bike a sexy look! Like Socrates said, "if your bolts aren't plugged, you should not listen to fake quotes from Socrates."
The plugs pop into 6mm and 1/4" stem bolts. Each pack comes with 10 plugs! Try out different colors!