True, but the OP's picture shows a "fixed" spacer - ie non-adjustable - so effectively its just a shorter horizontal dropout in his case (and in this case not for the derailleur claw since you can see the dropout has an integrated hanger).

I supposed one could move the spacer forward and tighten, but most of them seem designed to fit right up against the closed end of the dropout. And what if the optimal position for the RD is further back than the spacers allows (I know, take it out!)