As with all t-shirt applications, there are pros and cons as well as procedures to follow for best results.
Dye-sublimation heat transfer is the process of applying heat transfer dye (ink) on to a substrate, such as a poly-rich t-shirt. Dye-sublimation can give a long lasting transfer to a garment that does not add any weight or thickness to the end product. Unlike other applications like screen printing and direct to garment (DTG) methods these prints will not crack, fade or peel. When pressing on to the garment the ink infuses on a molecular level with the poly on your garment.
However, dye-sublimation will only bond to polyester or polymer coated substrates. You must use a poly-rich garment. I recommend at least 65% poly to 35% cotton or other mix. The heat transfer process requires a temperature of ~400°F for ~60 seconds. Some fabric content mixes will simply melt at this temperature.
Since dye-sublimation is a dye process, the darker the garment color, the less effective the end result will be. Before making a final commitment on color and prints it is best to try it out.