In the screenshot above, reps and sets are contextual fields - they don't add metadata to the node generally, just in your specific context.
Sometimes you want to add notes to a node without making it permanently part of that node. We call this contextual content, and it's available as columns in the table view and on items in the list view. This is great for planning projects such as:
Christmas present planning. You may want to reuse a list generated from a #person supertag, but you don’t want your gifting ideas made permanent in those people’s entries.
A vacation schedule. You don't want May and June to be part of the node Alex Strikha, showing every time you click the node. You just want it in this context: