Clover is not dangerous, but it can spread into lawn areas. It does fix nitrogen into the soil, and because of that some people actually like clover mixed with their lawn. The bees like it as well.

I would not call it a weed, but other people might.

Depends on the type of clover. The red clover that used to be grown for cow hay was found to cause cows to abort their fetus's. Talk to the locals, any plant where it is not wanted is a weed. I am not certain that the most common, Dutch White clover would grow well where it does not get a winter dormancy.