It’s easy to get carried away- look at how well these cubes stack and fill my suitcase! But when you bring too many cubes, you are more likely to fill the cubes with articles of clothing that you really don’t need.
I’d prefer to have 2 separate half cubes that can be mixed up a bit to find the ultimate best fit.
If you don’t fill your cubes, then there still may be room for the items inside to shift around and get extra wrinkled. If you overfill them, then it could make it difficult to repack, and let’s not forget about the extra stress on the zippers and bag itself.
You can definitely use packing cubes for more than just clothes, but chances are there is a much better packing container for things like cosmetics and electronics cables, and even bras.
Sure, it’s a bonus if you are able to fit more stuff into your carry-on because you’ve compressed said stuff in packing cubes. But fitting more in means you have heavier luggage.