The parent merely supports the child's hand so the child can point to letters on a board, typewriter, or computer in order to spell out words, sentences, and paragraphs. This method allows the child to communicate while he is simultaneously expanding and improving his ability to talk. This is a very important point since hurt children want to speak. They take a very dim view of using substitutes or special techniques that might bypass spoken language. In this they are entirely correct.
Every child has the right to speak.
Introducing this technique in no way diminishes that right or decreases the burden on us to find the best and fastest means of improving a child's speech. It is a very useful technique but it is not a cure. It will not change a child's respiration or improve his mobility and coordination. However, once a child can express himself in a more articulate way, it is often very clear that we have greatly underestimated his intellectual ability. This process of facilitation and communication opens our eyes.