GraphQL doesn't prescribe a particular approach to mutations; it allows the server developer to specify what mutations are available. For example, at Facebook we have a storyCreate mutation, and a friendRequestAdd mutation.
Mutations are just top level fields, but with side effects; because they are fields, the client sends up a selection set with the mutation. This allows the client to receive whatever data it needs to refresh, as the response to the mutation.
GraphQL was originally designed for reads, but we added write support to solve the parallel problem we were having with writes: different clients wanted different data back from the server after they performed a write. GraphQL gave us that capability.
Mutations are just top level fields, but with side effects; because they are fields, the client sends up a selection set with the mutation. This allows the client to receive whatever data it needs to refresh, as the response to the mutation.
GraphQL was originally designed for reads, but we added write support to solve the parallel problem we were having with writes: different clients wanted different data back from the server after they performed a write. GraphQL gave us that capability.