Characterization
Lance Sweets is brought into the series early in the third season ("The Secret in the Soil") as a psychologist to Seeley Booth and Temperance Brennan. The FBI forced them to seek therapy because Booth had arrested Brennan's father and the FBI was considering severing their partnership. Sweets' presence provides a bit of comic relief, as he is often the target of insults from both his clients, though they do show sympathy for him on occasion. His youth (according to Angela, Sweets needs to show his ID at bars to drink) and inexperience with police work also prove to be a challenge for him in the series, as many don't take him seriously, although his psychological analysis of Booth and Brennan is typically quite accurate. Booth is very suspicious of his ability to predict behavior using psychoanalysis, calling it "Jedi mind tricks". Also, while able to quickly recognize when someone is lying (Booth has described him as a "portable polygraph"), he himself does not appear to be very good at lying; when he lied about his personal life in "Double Trouble in the Panhandle", both Booth and Brennan were able to tell easily.
Sweets appears to be formally trained as a psychoanalytic psychologist, often referencing Freudian theories and approaches, even describing the psychosexual stages of childhood development to Booth. Ironically, Dr. Wyatt notes that "Freud has been largely discredited" in "Mayhem on a Cross", but still shows a great amount of respect and support towards Sweets.
He is also a quite capable piano player, as is shown in the episode "The Plain in the Prodigy", where he recognizes a collection of stones as a practice piano and proceeds to perform My Heart Will Go On, in a way that suggests notable skill with the instrument. He also briefly makes a living as a pianist in "The Mastodon in the Room". Oddly, in the episode "The Man in the Outhouse", while talking to Daisy Wick on the phone, he doesn't mention anything about playing the piano, but rather says that he plays "a little bass".
In the season 4 finale, "The End in the Beginning", he is presented as a bartender ("practically a psychologist") and the lead singer and keyboardist of a band called "Gormogon", a reference to a character in a previous story arc. He states he is not Gormogon and that it is simply a name; this may be a nod to a belief that many fans held that Sweets was, in fact, Gormogon. Even in this alternate world, Booth is still a father figure to Sweets, giving him the opportunity to audition at the nightclub, and Sweets is still in a relationship with Daisy. He is also protective of Brennan, having burnt evidence that he thought would implicate her.
Read more about this topic: Lance Sweets