Although the article discusses EXIF, which is primarily hardware-created metadata, there is the other metadata like Description and Keywords that I find very important (typically encode as IPTC or XMP metadata, if I recall correctly).

Especially older family photos that I scan: in the Description I can add what was written on the back (and/or front) of the photo. I use Keywords to identify who is in the photo as well as who I got the photo from (like a "Photo From Peggy" keyword).

In time when you get quite a collection, it becomes handy to be able to search your Photos library using this metadata. Also, when exported, the metadata remains if you allow it to. So when I send off digital copies to relatives, they also have that additional information.