The big advantage of using a power transistor as a heater is that it is its own control device. While a small resistor may be needed to limit the current, the power in that will be small. Most circuits, such as **broken link removed** only have 0.6 V across the resistor at most.
If you have a resistor as the heating element, and you want to control the heating in a linear way, then you can easily end up with more heat in the control device than in the heating element, so you will need a heatsink for the control element.
You can, of course, use the heat from the control device to heat the item that the resistor is heating. Then you have, at least partially, ended up with the transistor as the heater.