Deferred maintainence comes with a reduced value.

Apparent non-conforming use comes with reduced value.

Extended periods of vacancy comes with reduced value.

Frequent turn over (poor vetting of occupant) comes with reduced value.

Angry neighbors creates reduced value.

Good property management reduces deferred maintenance. 

Yes if not done properly the property value may decline and adjoining properties can also be affected.

It can have no effect, a decrease or an increase in property value depending upon the particular situation.

If they manage it poorly, there can be deffered maintenance or problems that develop with the house.  That can drop down the home's value and the value of homes around it.

# # If the PM lets the tenant damage the place, park derelict cars in the yard, use it for dealing drugs.

My first thought is, without good Property Management you could have a place that is run down, falling apart, and one that people want to move out of, as opposed to move into Minnette Olsen. 

I think Annette gave you a great answer.