Chazal say הסוכה מן פטור מצטער, meaning that when one has tzaar (discomfort or pain due to sitting in the succah), he is exempt from keeping this mitzvah. The Tiferes Shlomo taught that these words hint at one of the benefits we earn from keeping the mitzvah of succah. פטור מצטער, one becomes freed from his tzaros, הסוכה מן, when he performs the mitzvah of succah.
The Yitav Lev zt'l said that even if the decree on Rosh Hashanah and Yom Kippur was חייב, guilty, chas v'shalom, on Succos, the חייב can become roshei teivos for (Tehillim 149:5) ירננו בכבוד חסידים יעלזו, "The pious will exult in glory; they will sing praises..." Everything can turn around; there will be happiness, and good things will come to him.
The end of the pasuk is משכבותם על ירננו ,בכבוד, "...they will sing praises on their beds." The Sfas Emes (5653) says that this pasuk alludes to the הכבוד ענני, clouds of glory that protected Bnei Yisrael in the desert, and to the mitzvah of succah. He explains that משכבותם על ירננו refers to the mitzvah of succah because that is the only mitzvah we perform when sleeping. It is called בכבוד, for this mitzvah commemorates the הכבוד ענני. This mitzvah results in חסידים יעלזו, a lot of joy for the righteous because the mitzvah of succah brings salvation.
The mitzvah of succah is mesugal for a long life. The Ropshitzer Rav zt'l learned this from the pasuk (Vayikra 23:42) בישראל האזרח כל בסוכות ישבו, "Every resident of Yisrael shall dwell in succahs." The word אזרח is gematriya גבורה, mighty, and the pasuk says (Tehillim 90:10) שנה שמונים בגבורות אם, that the mighty live up until eighty. So, there is an indication in the pasuk that for keeping the mitzvah of succah, one will merit to live long.
