What theoretical disadvantage?

Working on the Caro-Kann, I ran into this statement by Fine in 'Ideas Behind the Chess Openings' (p.78):

'This defense is motivated by a desire to secure the good features of the French (prevention of any attack on f7) and to avoid the bad ones (cramped game, especially due to the fact that the QB is shut in). However, it is subject to the theoretical disadvantage of supporting a center Pawn (d5) not with another center Pawn (as in the French) but with a side Pawn. It thus becomes easier for White to get the upper hand in the center.'

I had never encountered the idea about the 'theoretical disadvantage of supporting a center Pawn not with another center Pawn but with a side Pawn'. Are there other examples of this?