Daf Yomi - Sukkah 9 - Intentionally nullifying a prohibition

The Gemara states that if one placed s’chach that is invalid for use on a Sukkah, such as branches that are still connected to the ground, the Sukkah can still be valid. This can be effected if he places valid s’chach on the Sukkah and there is more valid s’chach than invalid s’chach. The valid s’chach will thus nullify the invalid s’chach. The Taz to Orach Chaim 626 wonders how one can nullify the invalid s’chach by placing more valid s’chach, as there is a principle of ain mevatlin issur l’chatchila, one cannot nullify a prohibited matter outright. For example, one cannot place kosher food items into a pot that contains forbidden food items, thus attempting to nullify the prohibited food. The first answer that the Taz offers is that prior to the onset of the festival there is no prohibition in effect, as one is not obligated to dwell in a Sukkah until the festival commences. For this reason one would be able to validate the s’chach and he is not deemed to have nullified a prohibition outright. The Taz follows his reasoning with regard to nullifying chametz prior to Pesach. Alternatively, the Taz suggests that the principle of ain mevatlin issur l’chatchila, that one cannot nullify a prohibited matter outright, is only a rabbinical restriction that was instituted so that one would not derive benefit from his nullification of the prohibited matter. Regarding the mitzvah of Sukkah, however, one does not actually derive benefit from dwelling in a Sukkah, as there is a principle that mitzvos lav leihanos nitnu, the commandments were not given to derive benefit from. Thus, one is not deriving benefit from the validated s’chach.