Time is of the essence! Especially when someone is not breathing, their heart has stopped, or uncontrolled bleeding. A minute or two is the difference between life and death, and a firefighter/EMT is prepared and equipped begin life-saving procedures.
Medical equipment is carried on every fire truck, including heart monitors, defibrillators, Oxygen, plus support equipment to move a patient, splinting, backboards, C-colars, etc. Typically, not drugs, because of level of training (EMT, vs Paramedic), but a patient assessment is often relayed to the paramedics before they arrive.
In addition, there are more people to safely move the patient. Getting a 200+ pound patient down or up a narrow flight of stairs is not a 2-person job. Even for routine transports where only EMS responds, it is not uncommon to hear the fire department dispatched for "loading assistance".