Often, defendants want to try to represent themselves because: (a) they think they are smarter than everyone, including their attorney, the judge, the jury, and the entire legal system; (b) they think they'll have an easier time going off on whatever they want to do/say during trial, including long soliloquies, witness intimidation while being questioned, etc.; (c) they want to see every piece of evidence the prosecution has, which the defense isn't always willing to share with the defendant; (d) they think by representing themselves they can get their points across while never having to take the stand, in an effort to get the jury to sympathize with them but avoid cross examination; (e) they are basically delusional. (OK, the last one was an overstated joke, but even the best attorney in the world knows better than to represent him or herself!)
While the judge gives a pro se defendant some leeway during the trial proceedings, they are reined in. A pro se defendant isn't allowed to go off on rants, long monologues, harassing witnesses, etc. They're held to the same standards as an attorney, with some leeway for not having the training an attorney would have. It's a delicate balancing act for the judge, but on the occasional tv drama where you have a pro se defendant who seems to be given free rein in the courtroom are not real—they are what they are, tv drama.
While I haven't seen any pro se defendants in person myself, I do know enough judges to know they wouldn't let them run around doing what they wanted. Without doing further research this is all educated opinion, not concrete fact—that said, hopefully another attorney with a criminal defense background could weigh in and clear this all up. In the meantime, I'm hoping this will help quell any fears of what DP may attempt to do during the trial or sentencing phase.
