A few questions regarding perceptual filling-in of the blind spot

The fact that we are generally unaware of our blind spots is supposed to be the result of the visual systemfilling them in. This brings up the question of what would be the case if no filling-in were to take place.In other words, what would be the difference between the presence and absence of filling-in. The lack of aclear answer to this question makes it unclear what is to be explained by filling-in or even if any explanationis called for. Because filling-in is supposed to be accomplished by some ”mechanism” the lack of an answeralso raises a question regarding what is to be meant by ”mechanisms” in this case.