I've really never noticed this to be the case, as far as splices being preferred. I see the receptacle used the majority of the time in our area. I would imagine if the electricians are doing it in your area, its only because they think it is faster and thus $$. I have never had a screw connection on receptacle fail or a receptacle fail and not pass through power. It is not wired in "series" on the receptacle. In electrical terminology, in "series" has specific implications on how the various loads are handled (the voltage drop accross each load would depend on the loads present). A correctly installed receptacle with pass-through power using all 4 screws, would be considered wired in "parallel" in electrical terminology (since all the loads share the same voltage drop). I don't want newcomers to be confused by being lax with the vocabulary. I can understand how it is confusing, since the current must pass through the little tab on the receptacle. The difference is the current could have multiple paths (assuming something plugged in) and the little tab would be considered a conductor and not a resistive load.
Technically, that sounds correct. I can't verify it since I lack the more specific electrical knowledge.
However, my understanding of series is if you remove one of the outlets, you lose the whole circuit. With splices, if you remove an outlet you still have power (parallel).
Maybe the instructor could add something.