One of the main purposes of debate in the Buddhist training is to help you to develop decisive awareness (nges-shes). You take a position and then your debate partner challenges it from many points of view. If you can defend the position against all objections and you find that it has no logical inconsistencies and there are no contradictions, you can focus on that position or view with totally decisive awareness that cannot be shaken. We also call this state of mind firm conviction (mos-pa). You need to have this convinced awareness and firm conviction when meditating single-mindedly on any topic, such as impermanence, the equality of self and others, regarding others as more precious than oneself, bodhichitta, voidness, and so on. If you try to develop that convinced awareness on your own, such as through analytical meditation or just by thinking about the Dharma, you will never be able to question your understanding with as many objections as you can when a wide assortment of well-informed partners are debating with you. Others may find inconsistencies or mistakes in your logic more easily than you can ever do.
Further, debating provides a situation more conducive than meditation for beginners to develop concentration. The challenge of your partner in the debate and the influence of having classmates listening force you to concentrate. When meditating alone, only willpower brings you to stop mentally wandering or falling asleep. In addition, on the monastic debate grounds many debates take place very loudly next to each other. This also forces you to concentrate. If the debates around you distract you or cause you to be annoyed, you are lost. Once you develop concentration skills on the debate ground, you can apply them to meditation, even to meditating in noisy places.
Moreover, debate helps to develop your personality. You cannot remain shy, and still debate. You must speak up when your opponent challenges you. On the other hand, if you are arrogant or become angry, your mind is unclear and, inevitably, your partner defeats you. At all times, you need to maintain emotional balance. Whether you win or lose, the debate provides an excellent opportunity to recognize the "I" that is to be refuted. When you think or feel "I have won; I am so clever," or "I have lost; I am so stupid," you can recognize clearly the projection of a solid, self-important "me" with which you are identifying. This is the "I" that is a pure fiction and to be refuted.
Even when you prove to your debate partner that his position is illogical, you need to remember that this does not prove that you are the smarter one and that he is stupid. Your motivation must always be to help your partner to develop clear understanding and firm conviction in what can be logically proven.