I "get" sous vide cooking. I have--and regularly use--a cheapo FoodSaver for packaging and storing ingredients and food. And I even use a Vac-U-Vin canister (manual pump) for marinating.
Here's what I DON'T get: Since liquids don't compress or expand under vacuum, why would anyone buy a $$$ vacuum bagger for sous vide or any reason other than storing down comforters and sweaters? It seems to me that once the air is drawn out of the food bag, that's it--no vacuum, and no expansion of the food inside. In contrast, using a chamber with an airspace to which the food at least partially exposed, seems more likely to "open" the food, allowing some of the marinade to go deeper into the tissue.
Who can explain why one would need a $3K sealer for packets when a Ziplock would appear to do the same thing?