Take Bamboo for example. Many people place it in their garden for its aesthetic value and the privacy you gain from this living fence. Unfortunately most people do not realize that there are many different species of bamboo and the way in which each specific one grows. While some species grow in tight clumps and are easily managed, others create runners that spread in all directions, quickly taking over a garden and become a pain to remove.
While this is a frustrating experience for the person overrun with the bamboo, it actually makes it quite easy for the practical prepper to swoop in and get more bamboo than he could possibly use, often times completely free!
Now why on earth would you want to keep bamboo?