If you are selling a service, and in some case a product that has several features, then long copy works best. The buyer would want as much information as possible before parting with their dollar.
If you are offering a free product, then short copy is best. Users will trade trying to read what your product does to just using it instead.
If you are offering a free product, then short copy is best. Users will trade trying to read what your product does to just using it instead.