Bekhorot 43A

לפסול במקום אחים,

There is a practical difference with regard to disqualifying the widow, through his ḥalitza, from entering into levirate marriage in a case where there are other brothers. According to R' Yehuda, who maintains that this individual is certainly a eunuch whose condition is caused naturally, his ḥalitza is of no effect whatsoever, and therefore she may enter into levirate marriage with one of the other brothers. Conversely, according to R' Yosei, son of R' Yehuda, since it is possible that he is not a eunuch and his ḥalitza is valid, she is forbidden to the other brothers as their brother’s wife.

ולחלוץ שלא במקום אחים, איכא בינייהו.

And there is also a practical difference between their opinions with regard to performing ḥalitza with the widow in a case where there are no brothers other than this tumtum. According to R' Yehuda, ḥalitza is not necessary in this case, as she requires ḥalitza only if her late husband had brothers who are obligated to perform levirate marriage, and this individual is definitely a eunuch whose condition is caused naturally. By contrast, R' Yosei, son of R' Yehuda, maintains that he must perform ḥalitza with her, in case he is a male and not a eunuch.