Should you assign seats in a high school physics class? The theoretical arguments could go either way, with fundamental principles of teaching contradicting themselves.
Rule 1 of teaching high school: Never condescend, or give the appearance of condescending, to your students. If anything you do in class might possibly be phrased in a singsong voice that begins "Now boys and girls," you're screwed. Fair or not, students are almost looking for an excuse to act disrespected -- they are quick to feel like they're being treated like babies. A seating chart seems like it should fall under this proscription.
Rule 2 of teaching high school: Trust, but verify. We all know that it is in our students' best interest to do homework, and we want to trust them to be self motivated to do their homework; but we nevertheless collect the homework, at least if we want it done right. Suggesting that students read their text has a very different effect from "Tomorrow there will be a reading quiz on chapter 2.3, on which you may use your reading notes." The method of verification can vary, and certainly does not have to be grade-based. But, veterans know that any rule, suggestion, or good idea that's not backed up by some sort of verification is ignored.
Along those lines, a junior or senior in high school has been told many times that it is a good idea to sit at the front, not the back, of the room. It's a good idea to sit away from those who might distract them. It's a good idea to sit next to people who aren't necessarily best friends, to promote focus during lecture and to possibly create new friendships through the shared experience in physics class.
So, if you don't assign seats, what happens? The back rows fill up first, and friends (or couples or wannabe couples) huddle together. And no one changes seats after day one.
When it comes to assigned seating, I think rule 2 trumps rule 1. I've assigned seats only twice in my sixteen year career... but now I wonder why I went so long without assigning seats. I use "check your neighbor" questions often in class. Now that everyone's "neighbor" may or may not be a good friend, the discussions are more physics-focused, and less likely to devolve into a discussion of weekend plans. I insist on regular collaboration amongst the class. Once everyone has been forced to discuss physics in class with a random classmate, they become more comfortable collaborating with that classmate outside of class, too. And though I've rarely had major problems with classroom management, I find behavior to be even less problematic when seats are assigned.
In order to avoid the appearance of using elementary school methods on the first day of class, I present assigned seats as a fait accompli. I certainly do NOT allow folks to sit down anywhere, only to move them to an official seat a few minutes later. No, I've prepared folded index cards with each student's name on them. When a student arrives on the first day, he finds the seat with his name on it. End of story -- no discussion, no argument, partly because no one realizes that an argument might exist.
I've found it especially effective to switch up seating a couple times a year. I re-distribute seats quasi-randomly in the second trimester, and again in the third. So, when a student complains (whether disingenuously or not) that his assigned seat is not conducive to learning, I point out that the seats were assigned randomly, and that they will change in a couple of months. If someone does have a particularly annoying seat, like in the back corner of the room or next to an obnoxious person, then I'll be very sure he gets a prime ticket next trimester.