Augmentative communication

When I started out with PECS ,my mother was very apprehensive that it could impair his speech development.So are may people. My mother had her rationale to it.She felt if one makes it very easy to demand things with picture cards, why should he bother to talk?We have been assured over and over again by therapists whenever we use any aided communication,either verbal behaviour/ PECS, it doesn't stop him from talking. When you give a picture card for water,you stress on the word every time he demands for water.There are no substitutes for talking but these are crutches in some sense,it lowers the child's frustration and gives him an opportunity to communicate.