Difference between sequential and parallel divide and conquer
Just like you wrote, you can solve independent subproblems in parallel. Here are two examples:


In merge sort, you can sort the two halves of the input in parallel, and then merge them together sequentially.
In quicksort, you split the input into two halves sequentially, and can then sort both of them in parallel.


In the first case there is no divide step, and in the second case there is no conquer step. In other cases probably all three steps will be present.

Some divide-and-conquer approaches have a single subproblem. This is the case in binary search. Such algorithms do not benefit from parallelization.