Perhaps the best reason to look beyond Google Photos is redundancy. While Google is unlikely to implode anytime soon, there still the remote chance of server failures, or controversial new policies that might make you want to jump ship. You might even accidentally delete some of your material, in which case having copies elsewhere will be a lifesaver. I know Ive had to go hunting around on secondary services to recover files. Not very often, mercifully, but just knowing it an option provides...
