The binomial model breaks down the time to expiration into potentially a very large number of time intervals, or steps. With the binomial model it is possible to check at every point in an options life (i.e. at every step of the binomial tree) for the possibility of early exercise (e.g. where, due to e.g. a dividend, or a put being deeply in the money the option price at that point is less than its intrinsic value).