The Rishonim debate the question of whether one recites the Beracha of "Le’sheb Ba’sukka" each time he enters the Sukka, or only when he sits down to a meal. The Rambam (Rav Moshe Maimonides, Spain-Egypt, 1135-1204), in Hilchot Sukka (6:6), writes that a person recites the Beracha when he enters the Sukka, before he sits down. The Rambam makes no mention of eating in this context, indicating that the Beracha is not linked at all to eating a meal. The Maggid Mishneh commentary (by Rav Vidal of Tolosa, Spain, late 14th century) notes that this ruling follows the view of the Geonim, including Rav Hai Gaon (11th century), as well as the view of the Rif (Rav Yishak of Fez, Morocco, 1013-1103). According to this opinion, one can recite the Beracha of "Le’sheb Ba’sukka" many times throughout the day on Sukkot, as each time he enters the Sukka, he recites this Beracha. The Maggid Mishneh adds one qualification to this view, however, stating that one recites this Beracha only if he had left the Sukka for a significant period, such that he had "Heseh Ha’da’at" ("distraction") from the Sukka. If he left the Sukka just to get something from the house, for example, then even according to this view, he does not recite the Beracha when he returns to the Sukka.
Rabbenu Tam (France, 1100-1171), however, disagreed. He ruled that although the Misva of Sukka requires one to do in the Sukka everything he normally does in his home, nevertheless, the Beracha was instituted only for when one eats a meal in the Sukka. The Shulhan Aruch (639:8), surprisingly, does not bring the ruling of the Rambam and the Rif, as we would have expected. Instead, he writes that the accepted custom is in accordance with Rabbenu Tam’s position, to recite a Beracha over the Misva of Sukka only when beginning a meal.
The Taz (Rav David Segal, 1586-1667) explains Rabbenu Tam’s view by positing that eating constitutes the "Ikar" – the primary fulfillment of the Misva, whereas other activities are the "Tafel" (subordinate component). Although one is required to perform all his activities in the Sukka, the primary obligation is to eat in the Sukka. As such, the Beracha over eating covers the other activities which one performs in the Sukka. The Mishna Berura (Rav Yisrael Meir Kagan of Radin, 1839-1933) clarifies that although one might perform some activities after entering the Sukka before sitting down to eat, nevertheless, the Beracha covers those activities retroactively after it is recited. However, the Mishna Berura adds that one should recite the Beracha and sit as soon as he can after entering the Sukka.
The Taz’s understanding of Rabbenu Tam’s position could yield a number of interesting conclusions. First, the Taz boldly asserts that if one is not eating one day of Sukkot – for example, he dreamt a frightening dream, and thus observes a fast the next day – he recites the Beracha of "Le’sheb Ba’sukka" when he enters the Sukka, even though he is not eating. Since Rabbenu Tam’s view is based on the fact that the Beracha recited over eating in the Sukka covers other activities, one who is not eating throughout the day must the recite the Beracha when he enters the Sukka. Other Poskim, however, dispute this ruling, and understand that according to Rabbenu Tam, the Beracha of "Le’sheb Ba’sukka" was instituted only over eating in the Sukka.
Another example of how this question may affect the Halacha is a case addressed by the Hayeh Adam (Rav Abraham Danzig, Vilna, 1748-1820), of a person who leaves his Sukka and then returns in between meals. For example, a person left the Sukka after breakfast, returned in the afternoon, and will be going to recite Minha in the synagogue before supper. In such a case, the Hayeh Adam writes, the person must recite the Beracha over the period he spends in the Sukka in between meals. Since no Beracha is recited over eating during this interim period, this period spent in the Sukka is not covered by a Beracha, and the person must therefore recite a Beracha upon entering the Sukka, according to Rabbenu Tam. In practice, this is not the accepted custom. Nevertheless, Rav Natan Ben Senor (contemporary) recommends that if a person does spend time in the Sukka in between meals, he should preferably try to eat bread so he can recite the Beracha of "Le’sheb Ba’sukka" and satisfy all opinions.
In Sha’ar Ha’siyun, the Mishna Berura brings those who maintain that even according to Rabbenu Tam, one would recite a Beracha when he visits somebody else’s Sukka, even if he does not eat. The reason behind this distinction is the concept of "Teshbu Ke’en Taduru" – that the Torah requires treating the Sukka like one’s home. Just as a person generally eats meals at home, but eats light snacks elsewhere, similarly, Halacha requires eating one’s meals – defined as a Ke’besa (the volume of an egg) of bread – in the Sukka, but permits eating light snacks outside the Sukka. However, it is not all that common when visiting someone to eat a formal meal. Therefore, according to this view, even Rabbenu Tam would agree that if a person visits somebody, he recites a Beracha even if he does not eat, because in this instance, the "Ikar" is specifically not eating a meal, but simply being present in the Sukka. This view is brought also by the Aruch Ha’shulhan (Rav Yechiel Michel Epstein of Nevarduk, 1829-1908). It is told that Rav Aharon Kotler (1891-1962) was once in somebody’s Sukka when a guest arrived, took a fruit, recited "Boreh Peri Ha’etz" and then recited "Le’sheb Ba’Sukka." Rav Kotler commended the fellow for reciting the Beracha, in accordance with this view brought by the Sha’ar Ha’siyun.
Nevertheless, the commonly accepted practice is not to recite the Beracha of "Le’sheb Ba’sukka" unless one eats a Ka’besa of bread (or of "Mezonot" food, as will be explained in a different installment of Daily Halacha), even when visiting somebody else’s Sukka. This is the ruling of Hacham Ovadia Yosef, in Hazon Ovadia.
Summary: Although one is required to perform all his activities in the Sukka during Sukkot, the accepted custom is to recite the Beracha of "Le’sheb Ba’sukka" only before sitting down to a meal. (The precise definition of a "meal" with respect to this Halacha will be discussed in a separate installment.)