135:11 When a person is exempt from the mitzvah of succah but he does not leave it, he is considered a common (i.e., unlearned) person. (This refers to when there is an aspect of prohibition involved, such as when sitting in the succah makes him uncomfortable. This is considered a desecration of the holiday’s honor – Bi’ur Halacha 639:7 s.v. v’kol.) In such a case, one does not receive any reward for this, nor is he permitted to recite the bracha on dwelling in the succah because it would be a bracha recited in vain. When one leaves the succah because of rain, he should not do so angrily. Rather, he should depart humbled, like a servant who served a drink to his master only to have his master throw it in his face.
135:12 The practice is not to recite the bracha “leishev basuccah” except for a fixed meal. The accepted procedure is to first recite HaMotzi, then “leishev basuccah,” and then to taste the bread. Anything else that one may eat in the succah for the rest of the day, plus sitting there, sleeping there and everything else, is all covered by the bracha he recited for his fixed meal until he eats another fixed meal (when he would recite a new bracha). If one did not leave the succah between meals for his business or to go to shul, he does not recite the bracha again at the next meal. This is true even if one sat, ate, studied, davened and slept in the succah for the entire week of Succos: if he never left the succah, he would only recite the bracha once. This is because his attention was never removed from the mitzvah of succah. Even if he left briefly, with the intention to immediately return, it is not considered diverting his attention. (Some authorities disagree with this but in a case of doubt we do not recite a bracha – Shaar HaTziyon 639:86.) There is no reason to recite the bracha at the next meal unless one left to conduct his business, to go shul, and for similar such purposes. Even if one went into his house to study Torah or to do something there that causes him to delay, this is also considered diverting one’s attention and he would have to recite a bracha at the next meal.