Warning shots, shooting a fleeing suspect...
At my agency we're forbidden from firing warning shots. As far as the legality of shooting a fleeing suspect, the rule we're taught is it's legal only if they pose an immediate threat of violence (i.e. they're carrying a weapon, there are other citizens present for them to harm, etc.)
This, like most legalities, is subjective and gets evaluated and hashed out later in the shooting investigation, so you can't really give a "for example" scenario.