When it comes to sex between you and your partner, somebody else's desires or secret tricks don't matter. Wanna know what your partner likes? Ask them.
You are totally right saying "ask them". Unfortunately not all people find easy to share their sex fantasies openly, nor they like to be judged when they do, also they might just look for new ideas.
The use of Sexycrets should be to take away the aspect of communication that might make feel people uncomfortable selecting just the desires both of the partners like and sharing just those with them two.
That makes more sense.
I had no idea you were supposed to sign up with a partner and sexycrets would share the results. I'd make that more obvious on the front page.