Can Metadata/labelling or classification help me?

Pn1995 Yes definitely you can do using the appropriate labels as it will be robust approach. But if your need to share content with small set of users across different departments and with a frequent change of the permission or access needs then I might be refrained from using labels. I will use labels to assign permission for something like HR Repository where I share files for full-time, contractor and interns. Then I will assign different permission for each of them and then according to the label the content will be shared. The advantage is I don't have to manually add or remove people frequently and it makes the process robust and easy. SO if your need something similar you can use.

On the other hand if my need is designing a departmental a repository where a lot of people share information, we control and alter the user's permission frequently then I will use the SharePoint permission management to set unique permission for each file according to certain metadata. To automate the permission management I can write a workflow to set unique permission every time a document gets added.