What dramatic purpose is there in having 8 short scenes in the last act, Act V, of Shakespeare's Macbeth?

Thescenes in the last act shift from Lady Macbeth at
Macbeth’s castle to the march of Malcolm and the English forces to Macbeth in Dunsinane
to Malcolm and Macduff’s forces entering Birnam Wood to the attack on Dunsinane. The
reason for this is simply that you have many significant events occurring in different
places within a short period of time.

If I had to pick a
dramatic purpose, I would say this shows how all the events leading up to the last act
have caused all these events. And these events in Act V, while separate in place in time
are all bound to converge. This creates a determined synergy and as the tension
increases, Malcolm and Macbeth come closer to battle. The convergence of the scenes in
Act V mirrors the rising tension of the play. So, the form that the play takes with
these separate but converging scenes mirrors the convergence of
consequences.

You might also argue that this convergence is
affected by the supernatural aspect. Macbeth may only have been influenced by the
witches, but his actions have irrevocably led to this ending: as if it was fated or
inevitably caused by Macbeth's desire for power.

This is
part of the ambiguity of the supernatural role in the play. How much is determined by
fate and how much is determined by Macbeth’s own doing? In other words, all of these
scenes are separate but seem to be guided by some outside force, eventually to converge
with Macbeth's ending. What is guiding these actions? Is it the fate of the supernatural
influences or is it just the result of Macbeth's crimes?