I work in the film industry, so I understand how and why directors do things. Some of the deleted scenes in this film were not of good quality from a filmmaker's perspective. But of course the subject of this film was Asperger's, and the scene I referred to had cinematic value in and of itself. It dealt with subject matter not touched upon elsewhere in the film, subject matter which approaches one of the most defining traits of autism, what is referred to as "mindblindness."
One of the other deleted scenes, when Harlan shows Adam how to cut keys, and explains to him that he sort of has to BS a little in a job interview, and he doesn't really get it, was important too, but not as make-or-break as the scene with Beth.