In a shiur by Rav Zvi Sobolofsky on YUTorah called "Inyanei Sfeikos 12," Rav Sobolofsky discusses the
"בית המנוגע" (house of leprosy) and notes that while even though this is something the gemara says will never happen, there are nonetheless very important practical halachos that are learned from it.

For example:

• Chazakah - The gemara on Chullin 10b tells us the principle of chazakah (דמעיקרא) is learned from houses of leprosy.

מנא הא מלתא דאמור רבנן אוקי מילתא אחזקיה אמר רבי שמואל בר נחמני אמר ר' יונתן אמר קרא (ויקרא יד, לח) ויצא הכהן מן הבית אל פתח הבית והסגיר את הבית שבעת ימים

 

From where is this matter that the Sages said: Establish the matter on its presumptive status derived? Rabbi Shmuel bar Naḥmani said that Rabbi Yonatan said that the verse states [with regard to leprosy of houses that after a priest views a leprous mark]: “And the priest shall emerge from the house to the entrance of the house, and quarantine the house seven days”

(see said gemara for the full discussion)

• K'dei Achilas P'ras - This is a defined amount of time in halacha, approxiamtely 3-4 minutes (see: brachos). The source for k'dei achilas p'ras is ALSO derived from a house of leprosy; namely it's the amount of time required for one to become ritually impure when entering a house afflicted with leprosy. (see Succah 6a).

היה לבוש כליו וסנדליו ברגליו וטבעותיו באצבעותיו הוא טמא מיד והן טהורים עד שישהה בכדי אכילת פרס

 

If he was dressed in his clothes, and his sandals were on his feet, and his rings were on his fingers, he immediately becomes ritually impure, but they, the clothes, sandals, and rings, remain pure until he stays in the house long enough to eat half a loaf of bread.

Thus while a house with leprosy may not be practical, nonetheless the halachos learned for it are very much so- and presumably a Ben Sorer U'Moreh & an idolatrous city also have practical halachot/ concepts that are learned out from them.

In a shiur by Rav Zvi Sobolofsky on YUTorah called "Inyanei Sfeikos 12," Rav Sobolofsky discusses the
"בית המנוגע" (house of leprosy) and notes that while even though this is something the gemara says will never happen, there are nonetheless very important practical halachos that are learned from it.

For example:

• Chazakah - The gemara on Chullin 10b tells us the principle of chazakah (דמעיקרא) is learned from houses of leprosy.

מנא הא מלתא דאמור רבנן אוקי מילתא אחזקיה אמר רבי שמואל בר נחמני אמר ר' יונתן אמר קרא (ויקרא יד, לח) ויצא הכהן מן הבית אל פתח הבית והסגיר את הבית שבעת ימים

From where is this matter that the Sages said: Establish the matter on its presumptive status derived? Rabbi Shmuel bar Naḥmani said that Rabbi Yonatan said that the verse states [with regard to leprosy of houses that after a priest views a leprous mark]: “And the priest shall emerge from the house to the entrance of the house, and quarantine the house seven days”

(see said gemara for the full discussion)

• K'dei Achilas P'ras - This is a defined amount of time in halacha, approxiamtely 3-4 minutes (see: brachos). The source for k'dei achilas p'ras is ALSO derived from a house of leprosy; namely it's the amount of time required for one to become ritually impure when entering a house afflicted with leprosy. (see Succah 6a).

היה לבוש כליו וסנדליו ברגליו וטבעותיו באצבעותיו הוא טמא מיד והן טהורים עד שישהה בכדי אכילת פרס

If he was dressed in his clothes, and his sandals were on his feet, and his rings were on his fingers, he immediately becomes ritually impure, but they, the clothes, sandals, and rings, remain pure until he stays in the house long enough to eat half a loaf of bread.

Thus while a house with leprosy may not be practical, nonetheless the halachos learned for it are very much so- and presumably a Ben Sorer U'Moreh & an idolatrous city also have practical halachot/ concepts that are learned out from them.