The inkjet printer should be dedicated to sublimation, as the cartridges cannot be easily or cheaply switched with regular cartridges, for regular document printing.
Monochrome (single color) laser printers (like the HP III, 4 and 5) use a regular cartridge that has been re-engineered to deliver the special (dry powder) sublimation toner dye correctly. Like regular laser printer cartridges, laser dye sublimation cartridges only need ordinary copier paper for transfer printing.
Because a laser dye sublimation cartridge is completely self-contained, there is no problem in using the same printer, with a regular cartridge, switched back-and-forth to print regular documents also.
Except for the few shops trying to do T-shirts and ball caps, 95% of the work done in most sign shops is producing black print on gold-tone plates. Because of this, most shops use a monochrome laser printer for this type of work.
Not only does a laser printer produce faster and cheaper transfers than many inkjet printers, the images produced are a deep black. A black image from a laser sublimation cartridge will compare very closely to screen-printing.
Full color inkjets can produce nice colors, but it must be used on whites or very light colors. This is because the dye goes on much thinner with inks than with laser sublimation cartridges. This allows the gold color of a plate to "bleed" through the ink colors and produces a faded look. Even a silver color bleeds through ink colors (even when printing just black). But this can also produce some creative effects if used correctly.
This makes inkjets a good tool for full-color, personalized or short-run T-shirts, mousepads, mugs, etc. Single color laser printer sublimation toner is too powerful for "whites" and produces a noticeable background haze.
However, many sign shops doing sublimation are interested in producing small wall and desk signs, nameplates, badges, ID and legend plates and other items that are very profitable, but too small to weed. So dye sublimation becomes a very practical tool for this type of application.
Another reason is that those items more logically fit within the realm of what they are already doing, especially in the customer's mind. The more logically your diversification fits into what you are already doing, the more products you will sell. A tire company wouldn't be very successful selling flowers. It doesn't logically fit.
Last, but not least, is the fact that the profit margins on sublimated metal plates are equal to (and in many cases higher than) regular vinyl lettered signs, and adding the process requires a very small investment.
These facts make laser printer sublimation ideal for sign shops. After all, rule #1 in business is: Make Money. Every edge you give yourself just makes that job easier!