Digital sharecropping occurs when you build you online presence on a platform you don’t own (i.e. Facebook, Google+, Medium, Tumblr, etc.) The content essentially belongs to the platform, not you. This poses quite a significant risk to your longterm interests.
If one of these social media/blog platforms were to turn off its lights, your content would disappear.
If they changed the rules (as they do), your content would be subject to those changes.
If they became irrelevant, and people no longer went to the platform, your content falls into the darkness with it.
The guiding principle of building your online presence is simple: build your online presence on your own domain and host it using paid hosting.
Use these social media sites to share your content and lead back to your website. This will future proof your content and protect your audience from the whims of people who control those platforms.
For more information, I suggest you read this authoritative post on digital sharecropping by Copyblogger Media.