At a certain intersection there were three fatalities in five weeks. This is in addition to at least one accident per week.
A traffic study was performed and they determined a few things that everyone knows: a) no one drives the speed limit, and b) many people make a rolling stop and some don't even slow down.
The traffic engineers suggested a stop sign be placed at a much smaller intersection a half mile from where the accidents were occuring. This slows cars down, discourages through traffic, etc. Since the placement of the sign the number of accidents has gone down and there have been no fatalities.
Many residents in the area have questioned the stop sign, and some are even enraged. But hey - they're alive.
Also, if a city fails to take action where there are accidents they can be sued. So they have to place traffic signs in order to keep the lawyers at bay.
So when you see a stop sign that makes little sense, ask your City Hall about it. Chances are there is a good explanation.
(Of course, there are the signs that get placed because a prominent resident wants one. City Hall won't admit to those.)