Sometimes (though rarely) the bus stop is such that the bus can pull out of the traffic lane and become less of an obstruction, but even then, right turns are delayed significantly.
I don't mind this when I see a full bus, because I know that many private cars would slow down traffic at least as much. But damn is it annoying when the bus has 3 people on it (as is usually the case in my non-transit-oriented city).
They're fairly common in a lot of places, though only recently being built in the US, because they typically go together with having protected bike lanes, which were almost unknown in the US until recently. Here's a fairly typical example from Copenhagen (you can see that the bike lane passes behind the bus stop): https://www.google.com/maps/@55.6757297,12.5451953,3a,15y,46...
It is actually a deliberate policy in many cases not to have the buses pull out of the traffic lane, because it is hard for the buses to get back into traffic since cars do not want to let them in, resulting in slower bus journeys.
The number of cars removed from the road per bus is not dependent on the number of other cars on the road.
The number of cars removed is dependent on how many people ride in each bus and how many people ride in each car.
<wild speculation> I bet that number is about 6 passengers per bus, excluding environmental concerns. </wild speculation>
people_in_bus/average_#_people_in_cars = #_of_cars_removed_at_this_moment . Of course the model can be made significantly more complicated, but it's a good starting point.
Taking into account:
1) Number of drivers removed from the roads by average annual bus use
2) Size of the vehicles
3) Random acts of annoyance
4) Dangers posed by each
To confess my bias - I'm a huge fan of mass transit and a bike commuter who touches his car maybe once a week, but curious how else one might model this.