It also keeps the breakers all at the same height. We don't have the 42 breaker limit so some panels get quite large/tall if you mount them upright. For the record a few Canadian codes. 12 outlet limit on branch circutis unless fixed known loads attached. Smokes in bedrooms must NOT be AFCI. Lighting only permitted on 15 amp branch circuits. 20 amp circuits MUST use 20 amp receptacles. Either straight 20 amp or 20 amp T slots permitted.
