Bear with me - it makes sense!

I need to add custom fields to some projects - these fields are shared between projects in the same category. Say I have ten categories of project, each using their own custom field layout.

In order to have a custom field shared by more than 1 project, I need to create a global field and then quickly hide it in the default (system) field layout before anyone notices. This is not so bad, but then I have to go through every other field layout and hide the new field (before anyone notices), which is a bit of a git.

If you make the new field hidden by default, adding it becomes rather more manageable.