What makes you decide to not comment on a C/C thread? Do you open it, look at the pictures and see nothing wrong? Do you open it and not find the pictures interesting? No time? For me sometimes it's not so much as I don't see anything wrong, but I don't know the correct way to fix it, so I'll come back to it later hoping someone who knows has posted.
Like I said, I'm curious.
I am taking c/c to mean critique and comment.
I will not comment for several reasons
1) When I think that the request for c/c is just a disguise for really wanting to show off what they consider a great photo. This is often substantiated when someone does suggest a deficiency and the original poster replies with some sort of "are you crazy blah blah" That is proof to me that they were just trying to show off what they think is great.
2) When very similar to 1) the person owns very expensive equipment and wants the world to know it. They post a relatively nice photo and then list the pedigree of all the equipment that went into getting the photo. As if knowing the name of the mega dollar tripod somehow is necessary for the critique.
3) The photo was posted by a bored person just trying to generate some interaction to pass the time.
BUT if I perceive that a beginner is genuinely struggling to grasp some concepts then I will critique. Or if an advanced person is seeking alternative crop ideas for example that the poster had not thought of previously. Things like that will cause me to offer a critique.