Gonads do not include the vagina or penis. They are not gonads, and do not need to be touched to spay or neuter. Gonads are only the primary sex organs like testicles and ovaries.

The big benefit of removing gonads is that the body no longer produces as much of the respective sex hormone. This means you don't need to take estrogen or testosterone blockers for HRT, and the dosage of hormones can be lower. If you ever lose access to hrt, you don't get the full brunt of having your built in hormones take over.