EDIT: Thanks everyone, I really appreciate it! Sounds like they're mostly for organizing, I will ask her if she thinks they'd be useful before getting them.
I have an instinct for tetrising things into small spaces. My wife doesn't. When we travel by car, she tends to end up with many small bags holding the things that didn't fit in her suitcase, but the suitcase itself isn't packed super tight. (To be clear, I don't mind. I can't get my head around engines and electronics, and they come naturally to her. I think we've just got different brain structures for understanding this sort of thing.)
Are packing cubes any good for helping make things fit, if the geometry of that doesn't come naturally to you?
I ask because I'm considering getting her some packing cubes, if they might help with either making stuff fit or being able to find things in a more tightly packed suitcase.