The immediate benefit of a long running anime is that you’d always have something to watch. You grow with characters throughout your own lifetime, and their story becomes apart of yours.
Even though I said a lot of bad things throughout the month about Naruto, I love that show because it’s been apart of my life since middle school. I’m in college now and Naruto is still going strong. Fairy Tail is also a shinning example of a show that has lasted through multiple stories and a wide range of characters. Long shows have the ability to flesh out multiple characters whenever they please, because there is no need to rush anything.