Temple Grandin reported that if she was interrupted while giving directions, she was compelled to 'start over'...from the beginning. 

Seeing the big picture (the Gestalt) is a weakness for students with Aspergers Syndrome.  They are excellent at cataloging information in discrete form.  They are good at rote memorization too.  Above all, they are always looking for the patterns in the task at hand.  The world is a very confusing place...socially.  Patterns create order out of chaos.  It is very comforting for someone with Aspergers to have control over their environment.  That includes beginning and ending a task on their terms.  As it was for Temple, giving directions is rewarding in itself when one recalls the order of where to begin, which steps follow in order to the end.  Recalling the directions correctly and in order is a reward unto itself.

The typical person might be more (or only) focused on giving enough information to satisfy the person asking for directions.