Girls, who have a baby sucking on a pacifier, how do you understand th…

Girls, who have a baby sucking on a pacifier, how do you understand that he needs it? My little one has been sucking his hands lately. And I can't figure out, we first bought a regular nipple, just to check if he wasn't taking it. But here friends say that maybe he's too big in size, and they said to buy another one, so today my mother-in-law bought another one. He doesn't take it again, but sucks his hands ? even though he's full. In my opinion, he doesn't really need this pacifier. What do you think?