I travel A LOT and pack for myself and my husband. I am known by all my friends as a "professional packer". I can pack more stuff into a suitcase than anyone, which is great because I suffer from "travel anxiety" and tend to over-pack with just-in-case-I-need-this-item syndrome. And the Cubes and Pack-It-Folders help me pack whatever I "think" I might need.
I have every size of Cube and Pack-It-Folder...and use ALL of them for any length of trip; overnight to four weeks. I use the FULL-SIZE cubes for t-shirts, bathing suits, cover-ups, work-out clothes, jammies and underwear, socks etc. For short trips, I can use one cube and combine clothing. Longer trips I used multiple cubes for each type of item, i.e. there's one cube just for underwear...
I use the blue for my clothes and black for my husband, which is great to identify our respective clothing, when we share one big suitcase and when we share a dresser or shelves on a cruise ship.
We cruise a lot, so the cubes are great to pull out of suitcases and throw on a shelf and pull out clothes as you need them or in a drawer in a hotel room. I also use the Full-size cube to isolate one-day of clothing in a carry-on, in case luggage is lost or when we're checking-in and out of hotels every few days. It just makes it easier to grab one cube without rifling through a full well-packed suitcase to find stuff for one night.
I've been using Eagle Creek cubes for over 20 years, and have not needed to replace one that was worn out. I just keep buying additional sizes or more cubes to facilitate packing.