If we raise prayer flags... ~ Lama Zopa Rinpoche

"If we raise prayer flags, they bless the elements that touch the mantras, for example, the wind. Then, animals and insects who feel this wind are purified of their negative karma, and it transfers their consciousnesses to higher realms. Also, when rain and water touches the flags, it blesses worms and other creatures in the ground and liberates them from the lower realms."  
~Lama Zopa Rinpoche