When practicing emergencies, we are by definition adding risk. We do things we rarely do or have never done before. We fly with less than the full complement of equipment. We deliberately create distractions, then test our ability to overcome them. We venture into the far corners of our accustomed flight envelope and nibble on the edge of controllability.
The added risk exists, in part, because practicing emergency procedures has the potential to turn into a real emergency condition if the airplane, engine, or other component reacts to our actions (or improper actions, or inactions) with an unexpected response.
In the case of our twin-engine example, a simulated emergency (single-engine approach) turned into a delayed response to power application, which was then followed by a real-world VMC loss of control. Now, there’s a response for that VMC roll - because that’s an emergency procedure, one we are required to demonstrate on the multiengine rating Practical Test. Happily, the pilot and instructor at least partially corrected for the loss of control; although the airplane’s left wing impacted and suffered substantial damage, the two in the airplane survived to tell about it.