What Is the MATLAB `imreconstruct()` Useful For?
It could be useful in the field of OCR as a pre processing step.

Think about badly scanned data.
You'd like to convert it into binary image.
So the first step would be applying some kind of thresholding.
Since no thresholding is perfect, There will be some "Holes" / "Gaps" within the text.

Closing those "Holes" / "Gaps" can be done using morphological operations.

See example here: StackOverlfow - Adaptive Thresholding - Implementation of the Minimum Error Thresholding Method.