Example: MyCSS stores it’s styles in a file located in it’s installation directory. Naturally, when you share a single installation across blog instance, including all plugin files, you share that file, too, which is not what you want. That’s the major drawback.

I guess my experience has been that most plugins write to a Database table (such as saving the options for the plugin), so you get a fresh set of options on each blog instance — all with 1 install of the plugin.

But as you say in the next post, it’s true that plugins which write to a hard-coded file location would persist with the same across all the blog instances (if that plugin is activated).

The major drawback of sharing blog files is the inability to have individual blog data files per blog instance.

I’m not sure you defined blog data files? You defined blog code files, and blog database tables. The conclusion was confusing. What is the major drawback of a blog farm?

I understand you can’t have different (what I call) “codebase”, being WordPress itself. But you can have different themes per blog instance, therefore different PHP, therefore different blog files (blog code files & static files). So I haven’t figured out what the drawback is. Is it that you can’t have WP and Drupal as choices in a blog farm? OK.