To folder or not to folder ... that is the question

Good points, consistent with our experiences over the past 6 years. We 'de-promoted' folders in SP2010 and still in SP2013 in favour of Document Sets or metadata but, over the past couple of years, we've learned that Document Sets are good for specific purposes (for example, 'case files').

When users ask me about folders I say they are OK to use but try to keep the layers shallow, as noted - 2/3 deep only. One suggestion I give to users moving content from network file shares is to join up one or two-word folder names into single names. E.g., instead of Business Area - Meetings - Year - Month - Meeting date - Minutes as single folders, I suggest they try to roll them up as a single document library name: XYZ Meetings 2017, using one level of folders to separate the minutes.

Also, don't forget this lovely little option in all SharePoint document library views:

Whenever I see a document library full of folders, I enable that setting in a 'No Folders' view. It is a bit like a good magic card trick - suddenly users can see the 15 document they had buried in 400 folders.