I have seen very few freshmen that were big contributors on the varsity in any classification.  There will always be some, no doubt, and some of those will be solid but not big time studs as seniors. 
Jarrett Boykins was a very skinny freshman at Indy.  He did not go out for football, where he would have played JV, because he saw his friend Hakeem Nicks, a junior, as a varsity backup.  Two future NFLers and an SEC starter on the varsity.  Was disillusioned and played youth ball as a freshman getting some confidence.  Family moved into the Butler district.  Ended up being a stud as a senior developing with the weight and year round workout program.  Started at VA Tech, played for the Packers, and now with the Panthers.  Indy had a junior on the JV because he was just not ready for varsity, football wise, although physically he was a monster.  University of Maryland and NFL draft choice.  These are extreme cases but players given a chance to develop, play, and contribute on the JV are often the role players that eventually are huge contributors on the varsity.  As sleeh said numbers are important too.