From my understanding the proof of Thurston's hyperbolization theorem for Haken $3$--manifolds consists of cutting the manifold along a hierarchy (collection of incompressible, $\partial$-incompressible surfaces) to obtain a collection of $3$--balls. A hyperbolic structure is put on the $3$--balls, and then a bootstrapping argument results in re-gluing the hierarchy components so as to get a hyperbolic structure on the original manifold.
I certainly do not know the details for the above argument, but was wondering if there are any conditions on the hierarchy surfaces needed for the above argument to go through? In other words, are we required to choose a particular hierarchy to ensure that the re-gluing can be done consistently (or can one assume that any hierarchy will do ie- only the existence of a hierarchy is needed)? If a hierarchy with certain properties is needed, what are the conditions on the hierarchy?