In chessbase in the 7. Bc4 line of Gruenfeld's exchange variation, after:

1. d4 Nf6 2. c4 g6 3. Nc3 d5 4. cxd5 Nxd5 5. e4 Nxc3 6. bxc3 Bg7 7. Bc4 c5 8.
Ne2

8...0-0 and 8...Nc6, which more often than not transpose into one another, combined have been played over 10 thousand times.

8...Nbd7 on the other hand has only been played 14 times!  And yet it was used to defeat to Portisch in the Stockholm Interzonal in 1962, and Smyslov played it once later in the 60s.

Why such an immense disparity?  To me the main idea behind 8...Nbd7 seems to be to try to prove White's Bc4 is misplaced by following up with some combination of ...Qc7, ...Nb6 and/or ...c4.  Another motif, in particular in response to Bf4, is ...e5.

It seems like a viable way to play as Black, without having to learn reams of book analysis.  White will be on his own as of move 9, and depending on Black's preparation, well he may not be on his own until move 12-15.  As a club player, this seems a lot more appealing to me than having to learn all the theory behind 8...Nc6, only to know beforehand that both my opponent and I may be following the same theory until moves 15-18 or even beyond.