The only reason to use compostable bags is to promote the idea that one gives a crap about sustainability. The reality is that much goes into the production and distribution of coffee, but not much thought is given to what marginal difference packaging plays in the overall scheme. For instance, as a comparison, the manufacture and distribution of hair products sold in plastic containers. The container must be manufactured and then transported to the company that will label and fill the containers. The palletized cases of finished product are then transported to regional distribution centers, and then sent to warehouse distribution centers for large chains or small mom and pop stores. The carbon footprint is enormous for this type of packaging on a product everyone uses daily. A better alternative is for consumers to purchase bulk quantities in containers that can be reused or recycled easily, and refill point of use containers at home as needed. In coffee packaging these gusseted bags lay flat so that a shit ton of them can fit in a truck versus blow molded plastic containers. One can use rubber stamps to decorate the bags versus paper or vinyl label. And the gusseted bags can be kraft paper with a glassine type liner. These bags can be sent to compost just like anything else, and the liner which will not degrade is easily screened out of the product compost. This takes up minimal landfill. The same discussion was had about cloth diapers and disposable diapers. Cloth diapers with water use, required water treatment, etc., has a much bigger carbon footprint than if disposable diapers were sent to compost. The plastic outer shell would be screened out and discarded, but is minimal in comparison to the effects of water consumption and treatment for cloth diapers. Compostable coffee bags are a shallow claim for environmental concern for those that dig a little deeper, but are wonderful for marketing fodder.
