I was just wondering, if as Black I normally play the Caro-Kann and the Slav (but I slightly prefer the Caro-Kann), is it a good idea to answer 1. d4 with 1... c6!?
I looked in an opening database, but it looks like 1... c6 is extremely rare and is only played 0.3% of the time. What's wrong with it? Doesn't it just transpose into either a Slav or a Caro-Kann?
Does it have a psychological effect on weak opponents? Maybe they will be a little surprised, and thus they will take slightly more time to make their second move, and so it would be an effective subterfuge especially in blitz.