Die Spacer for Implant Crown and Bridge Cases?

Dr. K. asks:
When I send my crown and bridge cases to the dental laboratory, I specify how many coats of die spacer I want placed on my master dies. I used to work in a dental laboratory. Should we be doing the same thing for implant crown and bridge cases? For cement-retained cases on custom abutments should we be asking for more die spacer on tall abutments than short abutments? How should we manage standard machined abutments with a machined fit to the coping? The advantage of a machined fit between abutment and coping is the precision of the fit. But where is there room for the cement? If the components fit too precisely or too tightly, where is there room for cement? I am very perplexed about this problem. When I discussed this with my dental laboratory, the head technician told me that he recommends no die spacer for any implant crown and bridge.