Our brain do a lot of weird and wonderful things, like making us able to dive the the cars. They let us read a large number books. Our brains also do thing we don't want them to. Like skipping over over words or adding in word our sentences. Of course on reding a second time they are more noticeable. Like if you try reading this paragraph again.
Why do our brains do this? Well our brain cut out information that we don't need or our brains don't think are important as well as amplifying thing that are important or we are focusing on. People with autism can't do this and as such all five of their senses can overload them with information making it hard to concentrate.
So is it useful that our brains do things like this. In most cases it is but if your trying to solve a riddle or whatnot then no, it can be useless or even worsen your performance but overall it is useful.