It's very important in any CISM scenrio that a 'one-size fits all' approach is not used.
This has been my experience, the one and only time I've encountered it.
After a major incident, the whole watch was gathered together the next day: In turn we all described what we had seen, which did have its value in filling in the gaps which we all had regarding what had happened. However, then we had to describe how it had affected us. Some said how they had felt unsure about coming to work, some how they had slept badly etc etc, which I completely accept and understand. When it came to me, and I said that I was unaffected in any way, I was met with comments such as; "It will hit you at some point when you least expect it" and "as it was your birthday yesterday, you might suffer this time next year when something reminds you of it". I again said that I was fine, it hadn't affected me at all, and that luckily I'm the type of person who is laid back, relaxed and can move on with things very quickly. This was not accepted, and I felt like they believed I was trying to be macho and that it really had affected me.
Two and a half years on, and I'm still waiting for that sudden breakdown that I was told to expect (possibly while doing something as innocent as washing the dishes!).
So in my own limited experience, CISM appears not to allow the practitioners to accept that something hasn't affected you, and that if you claim it hasn't, then you must be wrong.