Advantage DO CONCURRENT against DO

Maybe this is a dumb question:

What advantage has a DO CONCURRENT loop compared to a normal DO loop? I understand that in DO CONCURRENT you are not allowed to use an index (i-1), but basically every DO CONCURRENT can be written as a normal DO loop (but not the other way round).

In the documentation the following sample code is shown

   DO CONCURRENT (I = 1:N)
      Q = B(I) + C(I)
      D(I) = Q + SIN(Q) + 2
   END DO

which can be written as

   DO I = 1,N
      Q = B(I) + C(I)
      D(I) = Q + SIN(Q) + 2
   END DO

Is the DO CONCURRENT construct faster or what is the advantage?

Another question: I remember that for parallel reasons it would be more effective to declare Q(N) too, so the DO loop can access Q(I) instead of just Q. Is that right?

Markus