Ever since Disney bought Lucasfilm and thus Star Wars, they ejected the old Expanded Universe. Those stories are now dubbed the Legends continuity. So since 2014 there has been a new continuty established where everything unless explicitly stated are in canon. This is all headed by the Star Wars Story Group and Pablo Hidalgo.
Though I haven’t been able to read all the books in the new canon, I have enjoyed the ones I’ve been able to sink my teeth into. It is a good way to fill in gaps that are skipped over in the movies. For example in Lords of the Sith it is set a few years after Revenge of the Sith and so we see the beginnings of the Rebel Alliance as well as the relationship of Darth Vader and Palpatine. We see that the relationship between the two has always had cracks in it and thus destined to fail. It helps explain as to why Vader would turn on Palpatine in Return of the Jedi.
Character backstories are also tricky to cram into movies. So Catalyst: A Rogue One Novel was used to help explain the backstories of Orson Krennic and Galen Erso. Two characters in the movie are introduced as already knowing one another but the details are vague (but not to the extent of throwing off people who don’t read the books). The novel fills readers on their long history with one another that the movie could only infer. So if you read the book right before seeing the movie, as I did, character interactions made a lot more sense and thus much richer.
Then there are the novels that do not fit either of those bills. Lost Stars is probably the best example of this as it is set right before the original trilogy and runs parallel and continues just shortly after. It is a Romeo & Juliet esque novel about two young people who find themselves on different sides of the Galactic War. Popular characters from the canon such as Leia Organa and Wilhuff Tarkin make appearances but they do not distract from the events of the novel and its protagonists. This is a good example of fleshing out the universe in unique ways that may not necessarily work anywhere else.
I cannot say that the novels are for everyone. What really is? Some may simply want to stick with the movies and that’s completely fine. Though others may want to experience more of what the Star Wars franchise can do. These are nice additions and well worth the read whether it be for a Star Wars fanatic or someone just wanting to dip their toes in the water.