Audio problem: When Hal is talking to Katrina, after he's been de-hypnotized, in the over-the-shoulder shot of him facing her, we hear him talking but his mouth doesn't start moving until he turns to look away from her.
Audio problem: In the restaurant, when Hal is standing at the hostess table asking about the booth before Mauricio calls on his cell phone, you can see the hostess' reflection in the small mirror or window next to her and the movements do not match. The mouth in the reflection opens to say yes before she does.
Answer: I think he was in the movie to reinforce that she is a genuinely nice person and that she had a wide circle of friends who appreciated her.