I think that to stay healthy in Crossfit, you definitely need to take advantage of the rest days.  Not even the regular rest days every week, but I occasionally, your body just needs a break.  For some reason, between the normal WODs and some that I've had to modify, I had to do hang cleans last Friday and Saturday and then we did them again on Monday and the back of my neck and shoulders were pretty beat up.  I finally decided to not even look at Tuesdays WOD and just take a day off.
I thought I'd be able to not even think about it but the Facebook community wouldn't let me go without thinking about it.  People started posting how horrible Tuesdays WOD was and how they had wished they had stayed home and how they barely even finished the WOD.  An average person would read these comments and be happy that they had missed out but because I'm crazy, I was actually a little envious that they had all got to go through this terrible torture together and that I wasn't there to partake in this painful experience.  I've apparently become a masochist maybe? I do see people that don't take rest days and I've even been tempted at times to skip the rest days.  I mean, when you feel good, keep it going right?  This along with skipping the warmups/cool downs has made Crossfit the best thing to ever happen to Physical Therapists and Orthopedic Surgeons.
Maybe I just need to stay off of Facebook on my days off too. Crossfit Facebookers are straight up crazy but I could fill up a whole other page going off on that.