Finding documents in Sharepoint online/Office 365 can be tedious. If you want to restrict your search to certain document types (like: reports, inquiries, CVs, sales orders, invoices) you either end up with too many irrelevant search hits (like: the search term "order" returns a lot of CVs) or relevant documents don't show up because the search term is not included (like "bill" instead of "invoice"). If you rely on Sharepoint's fulltext search capabilities then your users will be frustrated and spend too much time finding the right documents.

Frustrating search experience without meaningful refiners:

Entering the search term "order" returns a lot of irrelevant documents (e.g. a CV) and even misses some sales order documents.

Better: filter documents by type, language, etc:

If you provide search refiners, then the users will be able to precicely filter for all "sales order" documents, for instance.

Steps to improve your search experience with meaningful refiners:

Automatically tags entire libraries

Launch the automatic tagging process for all documents in a library (or a subset) in the "Tag documents"-dialog. Inspect the tagging progress and check the tagging report after the process has completed.