In practice, some units do quite a lot of Casevac, others none or virtually none. Partly disposition, partly to do with their patches. There are interestingly different interpretations of what Casevac means in practice. I am not sure how (paramedically) untrained police crews are supposed to be able to judge the state of a casualty that they have not seen............ In practice they don't of course.
In one of my former lives, we used to do about 15 CASEVACs per year on the Police Helicopter. To mitigate the risk we would contact the paramedic
at the scene to ascertain the condition of the casualty. Only if it was truly life-threatening would we transport and then only to a regional trauma centre.