Question on unique permissions count

Question

I am having a folder with 100 documents. Now I am breaking inheritance on this folder and applying unique permissions on it. Yes, all the documents under this folder will have same permissions as parent folder.

Now question is, if I apply unique permissions on a folder, it will treat as one unique permission or 101 unique permissions (since folder contains 100 documents)

Answer 1

It will be treated as one unique permission.
Setting folder permissions is a best practice, consider this article - Best practices for using fine-grained permissions:

Only set unique scopes on parent objects such as folders.

If you want to learn technical things, limitation and best practices regarding permissions even more deeply, consider also Best practices for using fine-grained permissions (SharePoint Products and Technologies) White Paper. It's old reading, however nothing changed drastically regarding permissions in SharePoint