Games, simulations, and role-playing are strategies to be considered when developing training. Games and simulations don't fit neatly into instructional design models because of the relative "fuzziness" of the associated learning objectives.
Games and role-playing exercises have long been used in classroom training. Typically, these involve dividing the students into groups of two or more, with each student assuming a different role, perhaps switching roles and repeating the exercise. One advantage is that these exercises can sometimes be developed relatively quickly. These types of exercises are especially useful for training used to modify behaviors, such as learning to use sales techniques. However, beware of a tendency to overuse this strategy at the expense of not truly covering the hard content that students need. Often, students will enjoy these exercises and rate the classroom experience highly, but did they really learn what they needed to?
For eLearning, game-like simulations can be developed that do not require multiple learners. These exercises can be fun for the learners, and may extend knowledge transfer in beneficial ways. Relatively simple games can be developed without a huge budget, but of course you could spend a small fortune developing a game or simulation that is highly polished.
It is usually wise to play down the hype that often accompanies discussion of gaming and simulation in training, and make reasoned decisions about the actual benefits versus costs.