Refinement of already-blended energy (the elixir) into the deep-center (of the cauldron/s) is a critical part of inner cultivation.  Definitely, one of the most important steps in all of alchemy.  You'll find emphatic references to this step in most, if not all, classical Taoist alchemical texts.  However, the cryptic poetry used in Taoist texts often occludes the meaning (and practical steps) from all but the already-initiated.

For me, the Tibetan text Tsongkhapa's Six Yogas of Naropa sufficiently clarified this topic, in surprisingly plain language, such that I understand the references in Taoist texts much better than before.  Highly recommended.

Three methods of working within the deep-centers:

1. Nourishing Pearl - Already-blended energy is brought and stored within the deep-centers, in the shape of a pearl.  This is deeply nourishing, and often brings an increased sense of personal stability, centeredness.  Fairly well covered in the HT system, except that as substance builds in the deep-center it has the limitation of inevitably expressing outwardly.

2. Refinement into Non-Duality - the energies "enter, abide, and dissolve" in the deep-center.

3. Jing to Light transformation - the energies interact with the drop / bindu in the deep-center, which initially produces light, and ultimately the drop leads back to, resonates with, Vast Light.

Although I list the above three separately, they're really not: They work together (even for the well-informed beginner) and gradually become fluently integral as you go along.  A tan tien ("medicine field") is a functional interplay of substance, space, and Light.

2 & 3 are gateways to the transpersonal; they have the potential to radically change the power and profundity of development.  Their culmination is not only a pinnacle of earlier work but, from a classical perspective, establishes Basic Ground.

~ Quote ~

"According to sutra the root of cyclic existence is our misconception that things have true existence.  According to tantra this [mis]conception and the energy wind on which it rides are responsible.  Since mind and energy are always together, tantric practice concentrates on halting the activity of the energy winds which serve as mounts for such [mis]conceptions.  By gathering these coarser energies into the central channel of the subtle body and by causing them to remain and dissolve there, their activity ceases as does that of the coarser mental states allied to them.  This allows subtle awareness to become active.  One of the main purposes of tantric practice is to make manifest the actual clear light, namely subtle awareness in a blissful state experiencing reality."

- The Three Principal Aspects of the Path, pg 42