PLNs give me the opportunity to connect with other like minded learners at the local, state, national and international level. One type of PLN I really enjoy are librarian blogs. It's facinating to hear the stories of fellow librarians. Some of them are funny, some are cautionary, some describe triumph and some reflect on defeat.
This type of network provides me with the needed connections to school librarians who share the same drive and advocacy that I have. These connections are endless. Overall, PLNs provide individuals with learning and access to leaders and experts around the world. These connections bring together communities, resources and information impossible to access solely from within school walls.
I strongly suggest if you have not developed your own personal PLN, start by reading Lisa Nielsen's tips for developing a PLN. Nielsen blogs at The Innovative Educator.