I was completely prepared to say that packing cubes were a waste of time for normal packers; they might be OK for neat freaks.
They ARE useful for project toting and storage, however: sewing projects in process, so you can keep all the bits together. Knitting and quilting that needs assembly.
And then I packed a rolling duffel bag for an out-of-town wedding. One of those whopping great shapeless rectangle spaces, where everything gets mushed and muddled and sinks to the bottom of the bag. I have a cube for underwear, one for exercise gear, one for street clothes and one for the dress & accessories I will wear to the ceremony. And everything stows, and won’t shift (much), and I will be able to find it when I get there.
I’m a convert.
These packing cubes turn out to also be great for packing motorcycle saddlebags. Makes it easy to load and unload, to keep his-and-her stuff separate, and to not have to rummage through everything in the saddlebag to look for those socks…