I'm not sure what you mean by "usefulness". Etsy shop owners often buy supplies from other Etsy sellers, as a way to support the community. Otherwise, I wouldn't buy supplies on Etsy, but it is not really intended for that purpose.
It's a venue for handcrafters and artists to sell their goods and support each other in a community network that works exceptionally well. It's a lot of work, as is any type of self-employment, but well worth the effort.
So, the 'usefulness' depends entirely on what your objectives are.