In today's Daf Yomi, Brachot 62a, it says:
It was taught in a baraita in tractate Derekh Eretz that Rabbi Akiva said: I once entered the bathroom after my teacher Rabbi Yehoshua, and I learned three things from observing his behavior: I learned that one should not defecate while facing east and west, but rather while facing north and south; I learned that one should not uncover himself while standing, but while sitting, in the interest of modesty; and I learned that one should not wipe with his right hand, but with his left. Ben Azzai, a student of Rabbi Akiva, said to him: You were impertinent to your teacher to that extent that you observed that much? He replied: It is Torah, and I must learn. Similarly, we learned in a baraita: Ben Azzai said: I once entered a bathroom after Rabbi Akiva, and I learned three things from observing his behavior: I learned that one should not defecate while facing east and west, but rather while facing north and south; I learned that one should not uncover himself while standing, but while sitting; and I learned that one should not wipe with his right hand, but with his left. Rabbi Yehuda said to him: You were impertinent to your teacher to that extent? He replied: It is Torah, and I must learn.
Clearly, both Rabbi Akiva and Ben Azzai knew that following one's rabbi into the bathroom was improper in general (with possibly a certain leniency to do it for learning Torah). After having already heard what Rabbi Akiva learned from following Rabbi Yehoshua, why did Ben Azzai feel the need to do exactly what his rabbi, Rabbi Akiva did, by following him - and in fact, ended up learning the exact same things?