My suitcase has a "compartment" for my suits so that is not an issue, but if they are effective, it could really free up some space in my suitcase. This is key because if history repeats itself, my girlfriend will take over my suitcase as well.
Two things that come to mind are weight (if you are flying) and getting the same kind of vacuum on the bag on board.
A Bad Day At Sea [with power] Always Beats A Good Day At Work
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
Princess: Ruby 2010, 2014, Caribbean 2013, Coral 2014
Since I found them, I never travel without them. I use the type that you roll so no vacum is needed. I have never went over on luggage weight which I was concerned about the first time I packed with them.
I can now use my two medium size cases instead of 2 large ones when packing for hubby and I. We purchased ours at Wal Mart and they were not expensive either. Well worth the money.