Packing cubes have been around for decades. It's about 20 years since I was a backpacker, and the enthusiastic shop assistants were trying to convince me to spend more than the value of my entire luggage on cubes to organise it in.
If you are packing once, travelling to one destination and unpacking into a cupboard, then they don't add much.
If you are going on a multi stop holiday, and will be rummaging around in your luggage daily, or living out of your backpack, then they really help to keep things organised.
I like the ones with clean/dirty sides. Otherwise I find that you can't stay organised because your clothes don't fit back in the same way they came out.
A cheaper option is to pack into big ziplock freezer bags.