Reading books increases your vocabulary because when you read your brain is actually learning some of the words whether you think it or not improves spelling/grammar,which can lead to a wider outlook on life, increased general knowledge, greater imagination (depending on what you’re reading though).For example say your reading a Darren Shan book this will help with your imagination.How? when you read description of a person e.g. Harkat (from the book) you imagine how he would look like in your head.But if you are reading something on science like say a revision guide that is knowledge.
When you read you pick up on the structuring of a paragraph without you even realizing it.You also learn different sentence openers.
When you are bored have nothing to do why not just read a book!