More often than not, when customers of plastic injection molding regard the mold itself, concerns revolve around dimensional issues. They are aware of mold fill, shrinkage, and just plain incorrect tool and die work being in play and possibly causing a dimensional issue when the mold is run and PPAP is processed.
The fact of the matter is, a great many things with regard to how the mold is designed and made can affect processing and visual criteria as well as dimensional issues. Plastic injection molding is a balance of mold, resin, and processing parameters. As with all variable systems, each of the three plays a part and in many cases, can make up for deficiencies in one or two of the others. All designs can either be robust, allowing wider variance with positive results, or fragile, requiring a narrow process window to achieve positive results.
Mold design needs to take into account many factors, to yield a robust design that a molder can make repeatedly, not just when making samples to get mold/part approval. Gate and runner design based on the proposed resin/composite are just two of the many variables.
The better your mold designer, mold maker, and processor communicate, the better your chances for a robust system. If you have ever gone into production on a part and a molder contacts you regarding part pricing saying the part is a higher cost than anticipated, it is likely not a robust design. Samples were manageable, but recurring production proves difficult.
If all three, mold designer, mold maker, and processor are under the same roof, long-term success is all the more likely. If not, get them talking so there is much higher likelihood of successful follow-on orders to initial start-up.