Firstly, I understand the idea behind HDR photography so I'm not looking for an explanation of HDR. What I'm interested in is the large number of exposures often used to capture a scene with high dynamic range. I understand that if there are three stops more of scene dynamic range than the sensor can capture that it makes sense to take an exposure that exposes for shadows and mid-tones and lets the three brightest stops clip and take a second exposure that is adjusted to ensure those highlights don't clip. This would appear to cover the full dynamic range of the scene. However in this situation, people often take extra exposures in between the two outer brackets. For example they might expose to a mid-point and then bracket at +1, +2 and -1 and -2.
Given that in this situation the two exposures overlap by seven stops, what is the advantage (other than safety bracketing) of extra exposures in between? If processed to increase dynamic range algorithmically rather than manually, is there a technical advantage to these extra frames? Often when I see people process multiple exposures manually, they will take the most correctly exposed image and blend in another image that captures the areas that were outside of the default image (for example the sky).
So long as the full dynamic range of a scene is covered by two images, what are the advantages of capturing more images in between?