There is another reason to organizing a classroom into individual desks. It helps a student stand or fall on his/her own merits. Teachers frequently pair up students to help those who are struggling. Used sparingly this can be a beneficial tool. Used too often, students find that they can lean on other students for answers. They learn to manipulate others into doing the thinking for them, instead of putting in the work necessary to develop their own abilities. Putting students into tables, or other configurations where their desks are together, imposes that situation. Not only does it increase the temptation to talk, poke, touch, or bother, it also makes it easier to cheat or at least use others instead of developing oneself through individual effort.
Some teachers use the excuse for grouping desks that they don't have room. They have filled much of the classroom space with things that are not nearly as important as having individual space for each child. Unwittingly they allow something of lesser value take priority over what is more important for the development of the student. A couch or "reading center" does not come close to helping the student as much as his/her own space and desk does. Shelves of books, manipulatives, or toys, tables of computers, etc., do not make up for the loss of the individual's space.
Is it wrong to place students in groups or tables? No, of course not, temporarily and sparingly. Salt really helps a meal, but a little bit goes a long way!