Some sites only publish extracts of their full articles. Reader View can fetch the full article text and show it to you in NetNewsWire, so you don’t have to go to another app.
There is a button to make this happen but I prefer using Shift + Command + R. I have a number of feeds this is super useful on.
Side note: I still want this fix. After chatting with the developers in Slack over several months and pleading my case it appears I will have to roll up my sleeves and submit a patch myself for this to happen. Which I understand. They have other priorities. But that likely won't happen until the snow flies. And my guess is that I'll have to re-learn Swift since it has been so long since I've written any.