I am not sure about this policy anymore actually. I think it was initiated by CF H Svcs Gp back about mid-2000s. I first recall it when I was at a HQ and it came out (as far as I can remember...). The intent was to keep people with the Flu or common cold, etc out of the CDUs during the initial 48 hours (most able to infect others during that time) for something they would just as likely be given a few days at home to recover.
At the unit I was at, Snr NCOs and up were able to authorize 2 x days 'sick at home' without a medical sick chit, on the 3rd day the mbr was required to report to the MIR. It was published in our ROs as such so the policy was clear.
I have heard of people (one of them was a Sgt at the unit I reported to when I OTd and was a Cpl again back in '07) who thought there was an 'entitlement' to 2 days off a month for sick leave, sort of like a civilian employee might get. I know of at least one case on my Wing and in my trade of someone who also believes this myth but hasn't be educated yet; that will happen at some point as everyone is bound to end up at the line sqn sooner or later.
Seems to me, the last few years or so people have been getting far better at just 'making stuff up' instead of finding and following official direction/policy. Not just on this topic, and a whole bunch of other ones too. The latest one I heard was the "you have to submit a leave pass if you are not sleeping within the geographical boundaries of base on the weekend" one. Yup, I'll just ignore that, thanks.
On another note, boys oh boys are we ever off topic the last few pages!! ;D