Two recent articles about life without traffic lights:

Marginal Revolution: Spontaneous order on the road

Matthew Yglesias » Uncontrolled Intersections

I recently made the same point about the five-way intersection near my house.
As the comments note, this isn’t truly “spontaneous” in that there are legal rules and social norms for behaving in the absence of functioning road control, but it does point out that in some cases (I would argue many cases, though not all) those rules, in some cases aided with a roundabout, function better than centrally planned traffic signals.
I think in large part it comes down to the original design and the current land use. When the intersection and adjacent land uses emerged prior to traffic signals, it may work better without. If it was designed in the modern era (e.g. a suburban arterial), it is more likely to require signal control, since that was implicit in its initial configuration. Three left-turn lanes imply traffic signal control. Retrofit is a kludge, which with proper timing may work on an urban grid (see Henry Barnes, but is less likely to work in a non-regular geometric road configuration (as in many European and some East Coast US towns). The effectiveness of traffic signals are context-dependent.