A baraita on our daf teaches that the mitzva of viduy – confession – begins on the eve of Yom Kippur at dusk. Nevertheless, the Sages recommend that a person recite viduy prior to the final meal before the fast begins, shema titaref da’ato ba-se’udah – lest he become “confused” during the meal.
Rashi explains that the concern is that the individual may become drunk during the pre-fast meal and he will neglect to recite his prayers properly in the evening. The Rambam, based on a variant reading of this baraita, explains that the concern is that the individual may choke during the meal and will not have the opportunity to say a proper viduy. The accepted practice today is for the individual to include viduy at the end of his Amida at minha prior to the meal, although the hazzan does not say it out loud during the repetition of the prayer. In addition, a number of special prayers and piyyutim are recited after the meal is completed.
The baraita continues, teaching that even though viduy was recited before Yom Kippur began, it is repeated during the evening prayers, again in the morning service (shaharit), the additional service (musaf), the afternoon service (minha) and finally in the special closing service (ne’ila). The individual who says viduy in his own Amida recites it at the very end of each prayer; during the hazzan’s repetition of the Amida, when it is said together with the entire congregation, it is recited in the middle of the prayer.
The Maharil Habib suggests in his Tosafot Yom ha-Kippurim that the difference between the individual and the congregation stems from the fact that the individual may not say his prayers with proper intent so he needs to include that transgression in viduy. The concern in the case of the repetition is that perhaps the congregation has fulfilled its obligation by listening to the hazzan, and if the viduy is left for the end they may no longer be paying attention.