Blocking is used in Much Ado About Nothing. Why has the director blocked the play in the way he/she has?
This is a difficult question to answer, since your question implies that you are asking about one director in particular, yet you don't make reference to any particular production. Each director of any play will make very specific choices about sets, costumes, and even the characters actions and behaviours (blocking) based upon their interpretation of a play.
Plays, by the very nature of the sort of work of literature that they are, are inherently incomplete, and must be staged in order to become the "complete" story. Blocking, or the staging of the actor's movements and placing on the stage, is a key aspect of what is missing in the script that is added in rehearsals for a particular production by a director. Yet, it is not possible to answer you question completely without reference either to specific scenes that are of interest to you, or mention of a particular production about which you would like a general critique of the direction.
An example in Much Ado of a scene that varies in terms of potential blocking choices made by the director is actually a scene that is not in the script at all -- the deception of Claudio and Don Pedro at Hero's window. Don John tells these two in Act III, scene ii that if they will come with him, he will show them proof, by their own eyes, that Hero is unfaithful. Don John is planning to have his henchman Borachio lure Hero's waiting woman, Margaret onto the balcony and woo her under the name of Hero, while the other three observe from below.
This scene is not included in the play that Shakespeare wrote, but is often staged by directors so that the audience might see, along with Claudio, the ruse that Don John has cooked up. Directors will use the staging of this invented scene to either make Claudio more or less gullible when it comes to his accusations, based upon how believable the wooing of Margaret (as Hero) appears to be.
This is one example of where a director's blocking makes a statement about the how the audience is intended to experience the behaviour of the characters, but certainly there are others, as there are in any play.