Ibn Majah

Benefit:
Sitting on the heels is the translation of "iq‘a’."
There are two forms of iq‘a’.
One form is prohibited and one is permissible. The prohibited form is to sit with the shins upright, the buttocks placed on the ground, and the hands resting on the ground.
This form resembles the sitting posture of a dog.
Therefore, authentic ahadith support this weak hadith,
because in authentic ahadith, it is forbidden to sit in the manner of dogs and wild beasts.
The permissible form is that, while sitting between the two prostrations, both feet are upright and one sits on the heels, while the shins and knees are on the ground.
This is what Abdullah ibn Abbas radi Allahu anhu has declared to be Sunnah. (Sahih Muslim, al-Masajid, Chapter: The Permissibility of Iq‘a’ on the Heels, Hadith: 536)