I mean, I read that Lucas thought of R2D2 as the MacGuffin of “A New Hope”, and thought that it was important for the audience to care deeply about him. And it worked. However, as a film device, I think it’s more important that the audience cares that the protagonist cares about the MacGuffin. I still don’t know why I should care about the Maltese Falcon, but I know that Bogart certainly cared. And for me, that was enough to make the story compelling.
I do agree though about Pulp Fiction. The briefcase was a very meta reference where the audience is assumed to know what is going on. And in that case it helped to provide a common thread through the different plot lines. But from a higher level, it was done with a wink and a nod to the audience. It was basically using the MacGuffin as a foil to use as the “typical linear storyline” when what Tarantino was really doing was playing with time lines and points of view.
After all, its a Tarantino film. He basically expects the audience to be familiar with film theory (or at minimum: expects the audience to already be familiar with "typical plotlines").
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Your typical action movie / popcorn movies: Raiders of the Lost Arc (The Arc of the Covenant), Mission Impossible (The Rabbit's Foot), and Men In Black (Orion's Belt), and pretty much every James Bond movie, has MacGuffins galore and are better examples of it.
The scriptwriter doesn't care about the MacGuffin. But a well written story has the __audience__ care deeply about it. Otherwise, the escalation and conflict has no purpose. Pulp Fiction / Tarantino used the briefcase as an exercise in how to make the audience care for an object, despite never really explaining why that object is the center of all this conflict.
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Golden Fleece, Apples of the Hesperides (aka: Heracle's 11th task), Holy Grail. It doesn't really matter what these objects do, we just use them as storytelling devices to get the characters thrust into conflict.