1. One may conduct himself in a stringent manner only when there is an opinion that requires that particular stringency.
2. One may be stringent if he is unsure about the Halachah.
3. Rav explains the dispute between the Tana Kama and Chananyah (from Daf 6a).
4. Rav Yosef quotes Rav Yehudah who discusses the law in the case of a Mavoy that leads into a backyard that leads to a public domain.
5. Abaye says that Rav Yehudah's teaching (#4) could not have been taught to him by Rav.
A BIT MORE
1. One may not follow the stringencies of two different opinions, when those stringencies contradict each other. One who follows two inconsistent stringencies is called "a fool who walks in darkness." (See Ritva.)
2. The Gemara notes that Rebbi Akiva was unsure about whether Beis Hillel said that the cut-off date for Ma'aser of an Esrog is the first of Shevat or the fifteenth of Shevat. He therefore was stringent to separate Ma'aser twice (Ma'aser Sheni and Ma'aser Ani) from an Esrog that he picked on the first of Shevat.
3. He explains that they disagreed only about how to make an Eruv in a case where the Mavoy is open on both sides to a bona fide public domain. However, if it is open only on one side to a public domain, everyone agrees that doors are not required and that a Tzuras ha'Pesach and a Lechi suffice.
4. If the Mavoy has three walls and it leads into a backyard that has four walls (besides the entranceway that it has into the public domain), all that is necessary to permit carrying in both the backward and the Mavoy is a Lechi or Korah at the entranceway to the public domain.
5. Rav Yosef replies that Rav Yehudah himself clearly agreed with this position, since he ruled this way in practice in a case that was presented to him. Rav Yosef adds that although one could say that Rav Yehudah heard this from Shmuel, he also could have heard this from Rav (as Rav Yosef proceeds to answer Abaye's question).