Don’t know why you are being downvoted, it’s a genuine question. Just generally the control groups for a vaccines effectiveness when given to the public, example, comparing the spread of a virus to those vaccinated and unvaccinated, or comparing the severity of symptoms between the 2 groups.

I mean, these are ment to imply that you have become a hazard and stopping in the middle of the road do be pretty hazardous.

Legitimate reasons to use it imo is If you’re gonna be stopped for less then a minute on the side of a road, otherwise find a park, if you need to stop and not somewhere you can park, get as far off the road as you can (ie shoulder of a freeway) or if you actually are in an emergency and need to stop, e.g. you’re car is suddenly externally combusting