Here is a straightforward explanation about the usefulness of decodable books for children learning to read.
‘The look on children’s faces when they realise how easy reading is – knowing the sounds and connecting them to graphemes on the page. I call decodable text the ‘no tricks books’. They are so simple to use for both teachers, parents and children and importantly decodable text is supported by evidence-based research )from the US, the UK, and the National Inquiry into Teaching of Literacy in Australia.
http://www.teachermagazine.com.au/article/teaching-and-using-decodable-text?utm_source=Twitter&utm_medium=Social%2520media&utm_campaign=Teaching%2520and%2520using%2520decodable%2520text
Thanks to Susan Godsland of www.dyslexics.or.uk for flagging up this article by Maureen Pollard.