A hot rail will vaporize the stimulant in question, allowing both the blood vessels in your lungs and nose to absorb the drug. It is more efficacious that both intranasal and smoking. For example, if a .1g of meth were snorted, then undoubtedly some of it is going to fall out of your nose, drip down your throat, not absorb the full amount. Smoking .1g would take a few hits before it was finished. With a hot rail, thay .1g can be "smoked" in a single hit via your nose and allow more absorption from both nasal and lung blood vessels.