Here's a nice little walkthrough for when you should call the cops:

Severe Injury/medical emergency -> No, you should call an ambulance.

Car Crash -> Fire department and ambulance

Mental Health Crisis -> Community healthcare network. 211 in most communities, or find a local community group dedicated to that care

Fender Bender -> Get yourself to a collision centre. They don't give a shit.

Crimes -> You can try the non-emergency line, but they're not gonna show up or even call back. Enjoy being on hold for 3 hours.

Someone who's an active danger to the public -> That is the cop.

There's no reason to call the cops, or for them to exist in the first place.

@mayintoronto several years ago, someone tried to run me down with their car while I was walking on the sidewalk. I got a photo of the car and license plate and noted which direction they tore off in. I called the cops. They said they'd send someone right over. No one ever came. The car was parked on the same sidewalk the next day.
@Shanmonster Useless. We could be doing so much with our city with all that money we waste on cops.