For overnight or 2-3 nights, packing cubes might be unnecessary - but they do keep things organized. We find them useful especially when traveling for longer duration - fewer minutes to unpack and/or just transfer them onto the hotel drawer/dresser, etc.

Smaller: slim, 1/2 sized & 1/4 sized cubes are useful for keeping gadgets, medicines, and other "loose" items together - combined that with rolling, to fit amazingly quantity into a 22" MLC (for mine, hers on rollers.) - with a mix of eBags and Eagle Creeks. For the personal bag, 2 Tumi (Delta's freebies) hold the dry toiletry & medications plus the wet 3-1-1 if security screening is involved for the trip, and maybe the slim gadget pouch, for long haul in-flight use. A zippered pouch will hold the wallet, keys, loose change, smartphone, pen & tissues, etc. together at "checkpoints" without getting lost or forgotten. They worked for me as an interchangeable system, a quick glance of everything in place and out the door in 5 minutes flat or less.

Some folks like/prefer those "space" bags for similar reasons. The keys to making them work is to use it to compress the contents & keep them tightly packed, it won't shift or move around - that leave extra space around the bag to "squeeze" other roll items to fit. Dirty/soiled items get rolled up into those hotel laundry bags before returning to the packing cube (to minimize/keep out odor.)

It's a matter of YMMV - give it to try, no longer does 90% of the content inside the bag spilled onto the floor/sidewalk, etc. especially when rushing. eBags offer free return including shipping, no questions asked & let UPS bring them to your doorsteps or check out EC at a nearby outdoor/sporting good stores.