So what is the difference?

Basically Ghost(Pro) is a web app online that you just sign up for and create an account in to get started. It comes with as small monthly subscription fee and you can be up and running in seconds

A self-hosted Ghost instance is a package that you need to install yourself, on your own server environment. You also have to make sure your server environment has all the necessary support you need to run Ghost e.g. the server javascript framework, node.js.


THE PROS's & CON's

Ghost(Pro)

It's like creating an account on a web app, (e.g. Facebook), and once you have an account you can access your admin panel that you'll use to manage the blog.

THE PROS

  • The Ghost folks take care of EVERYTHING ! (^_^) !
  • Free updates for life and you'll never have to worry about having an outdated version of Ghost
  • Hosting and server maintenance is included
  • Because Ghost is a non-profit, all of the money made on hosting goes back into the platform itself

THE CONS

  • There is a monthly minimum fee of USD19/month, (which personally I think is fair), but may be steep if you are just starting out and are not making money yet with your blog
  • You don't have access to the file system of the server in case you want to dig deeper under the hood

Self-hosted Ghost

Basically you install and host on your own server and hosting environment.

THE PROS

  • Free
  • You have complete access to the file system of the server in case you want to dig deeper under the hood

THE CONS

  • You have to maintain your own server
  • You need to update Ghost by yourself
  • Hosting and server maintenance fees are something you pay separately for
  • Not many hosting providers offer the necessary specs to host a node.js app like Ghost. A regular VPS with a cPanel will usually not cut it.

WHAT TO EXPECT WITH BOTH SOLUTIONS

Ghost(Pro)

A super-quick setup, wonderful support and great manuals that teaches you how to use the admin interface.

Self-hosted Ghost

Some confusion here and there when installing but with the help of the wonderful support community, every issue will be resolved and at some point you'll have your own Ghost blog. It can be as quick as a few minutes or as slow as a few hours depending on your technical knowledge domain.
If you have ever set up a Wordpress blog or some other CMS, this will be a breeze.

THE GOOD NEWS

If you decide to self-host you'll find that this web site will cover a lot of useful information on how to go about it, including lot's of gotcha's that can otherwise stump you. I suggest you start here

Reference Links:
https://ghost.org/ghost-pro-vs-self-hosting