illegal low level flight causes a lot of accidents...especially here in australia on hot days.
Here you must be 500 ft agl and 1000 ft agl over built up areas, with a 600 m lateral boundary applied to built up areas for the purposes of the built up areas requirement.
The exception is t/o and landing, and low level commercial work such as spraying, and airshows...the latter is by permit only.Emergency would be the only other exception, but not emergency training. There may be an exception for rotor training but i dont know.
The big killer is high power lines.