Chagigah 11A

בגזבר המסורות לו אבני בנין עסקינן, דכל היכא דמנחה ⁠— ברשותא דידיה מנחה.

Rather, we are dealing with the treasurer of the Temple, to whom the consecrated building stones were transferred for safekeeping. The reason for the exemption is that anywhere that the stone is resting, it is considered to be resting within his domain. Consequently, he is not liable for picking up the stone or beam, as he is permitted to carry it. However, he does not have permission to give it to someone else, and therefore when he hands it over to someone else he has misused consecrated property. If so, this halakha is also perfectly logical and should not be considered like mountains suspended by a hair.

אלא מסיפא: בנאה בתוך ביתו ⁠— הרי זה לא מעל עד שידור תחתיה בשוה פרוטה. מכדי שנויי שנייה, מה לי דר ומה לי לא דר, היינו כהררין התלויין בשערה?

Rather, the comparison of these halakhot to mountains suspended by a hair is based on the latter clause of that same Mishnah: If he built the stone into his house, he has not misused consecrated property until he dwells under it an amount of time that is worth a peruta. Since he has changed the stone by incorporating it into his house, what difference is there to me if he resided there, and what difference is there to me if he did not reside there? Apparently, this is the halakha considered like mountains suspended by a hair.

ומאי קושיא? דלמא לכדרב. דאמר רב: כגון שהניחה על פי ארובה. אי דר ביה ⁠— אין, לא דר ביה ⁠— לא.

The Talmud rejects this claim. And what is the logical difficulty with this halakha? Perhaps it is stated in accordance with the opinion of Rav. As Rav said: This Mishnah is referring to a case where he placed the stone over a window, but he did not make any adjustment to the stone itself. If he resided in the house, yes, he has misused consecrated property, as he derived benefit from it. If he did not reside in it, no, he has not misused consecrated property, as he gained no benefit from the stone.