מִי שֶׁהָיָה רֹאשׁוֹ וְרֻבּוֹ בַסֻּכָּה, וְשֻׁלְחָנוֹ בְתוֹךְ הַבַּיִת, בֵּית שַׁמַּאי פּוֹסְלִין, וּבֵית הִלֵּל מַכְשִׁירִין.
אָמְרוּ לָהֶן בֵּית הִלֵּל לְבֵית שַׁמַּאי, לֹא כָךְ הָיָה מַעֲשֶׂה, שֶׁהָלְכוּ זִקְנֵי בֵית שַׁמַּאי וְזִקְנֵי בֵית הִלֵּל לְבַקֵּר אֶת רַבִּי יוֹחָנָן בֶּן הַחוֹרָנִי, וּמְצָאוּהוּ שֶׁהָיָה יוֹשֵׁב רֹאשׁוֹ וְרֻבּוֹ בַסֻּכָּה, וְשֻׁלְחָנוֹ בְתוֹךְ הַבַּיִת, וְלֹא אָמְרוּ לוֹ דָבָר. אָמְרוּ לָהֶן בֵּית שַׁמַּאי, מִשָּׁם רְאָיָה, אַף הֵם אָמְרוּ לוֹ, אִם כֵּן הָיִיתָ נוֹהֵג, לֹא קִיַּמְתָּ מִצְוַת סֻכָּה מִיָּמֶיךָ:
One whose head and the greater part of his body were within the sukkah and his table within the house: Bet Shammai say: it is invalid and Bet Hillel say it valid.
Bet Hillel said to Bet Shammai: Did it not in fact happen that the elders of Bet Shammai and the elders of Bet Hillel went to visit Rabbi Yohanan ben HaHoroni and found him sitting with his head and the greater part of his body within the sukkah and his table within the house, and they didn’t say anything to him? Bet Shammai said to them: From there [you bring] proof? They indeed said to him, “If this is your custom, then you have never in your whole life fulfilled the commandment of the sukkah.
I don't understand the importance of the Maase here: There were two schools, they went to meet another Rabbi to [probably] seek a confirmation. [turned out] He followed B"H. Then B"S told him that he never fulfilled the Mitzvah according to their approach.
What's the point of this long story?