No, as other comments in the thread have pointed out, you can easily have an SQLI that doesn't send information back to you. You may find value in changing what's in the database even if you can't read from it.

If you do have the ability to retrieve information, then one of the first things you'll do is retrieve the schema.

And the reason you'll retrieve the schema, if you can, is that it facilitates the attacks you actually want to make. It has no value to you other than enabling your attacks. This observation seems sufficient to answer the question "does knowing the schema enable attacks?".