Here is my understanding of this custom function.
If I check "spot" metering for AE locked after focus, then I can lock the exposure when the shutter button is pressed halfway to focus. Then I can recompose the image using AE (perhaps evaluative) and Auto ISO. The new compostion will now register new AE and Auto ISO.
With my test images I discovered that a very bright background with a dark object in the foreground can both be captured and will show details. Without this AE lock after focus, the very bright background is blown out when I focus on the dark object in the foreground.
As anyone else played around with this?