It's meant to be fun and encourage reading as a good thing which is sometimes challenging but mostly enjoyable. It helps children realise that an important part of reading a book is understanding what's going on, that you can interact with books by building your expectations of the action and by predicting what's going to happen next, etc, etc.
For the parents in a rush though, books without words are painful and you're never quite sure when a page is "finished" are you?
I always found ORT books had pictures that the children wanted to decode before reading even when there were words on the page. Some nights I'd be repeating through gritted teeth "look here are the words, let's READ them now shall we" - and feeling guilty because I was killing the enjoyment of the book. I just wanted to get a few pages done and write it down to show we'd done it (how mad is that?).
HOWEVER, please don't worry about rushing on, read loads of things at home with your dd as well and she can practice reading letters/words that way if she wants to. There aren't that many books without words in most schemes so you'll be over them soon and the skills they're trying to build are so important to how your dd will interact with books for the rest of their lives.