Let me phrase it in another way. If you're writing a crime thriller or murder mystery for example, there must be something in your mind other than the murder and subsequent investigation and hopefully arrest of the culprit. That's just story for the sake of story, in this case mainly police procedure. Ask yourself what type of feelings you're hoping to elicit from the reader, how do you want them to feel at certain stages of the book. What's the overall message? What is the one thing you want your readers to take away from the book when they've finished? Is it just satisfaction at the conclusion of the investigation?
Once you've answered the above questions they should be your focus throughout the writing process. Yes you should have a sound timeline, a well thought out and detailed investigation, but you should always have in your mind what you originally set out to achieve. It could be that you want the reader to feel sorry for your main character, or even for the down on his luck criminal. Perhaps you want the reader to go on an emotional rollercoaster of a journey throughout the story. Or maybe you want to take your reader from rooting for the detective to rooting for the unfortunate criminal.
Whatever it is you're trying to achieve, whatever emotional response you want your reader to exhibit, that should be the focus of your novel. One could argue that the crime and investigation itself is simply the vehicle through which you choose to elicit your reader reaction. It's the same for romance novels or erotic fiction. It's not enough to write a sweet story, or some steamy sex scenes, because you may be forgoing a better way of telling a story to create that all important reaction. If you want fantasy escapism, how bogged down in the banality and mundanity of life can you make your character initially? How much can you beat them with the cruel stick of fate before you give them their break?
If you want to create a great character, one that can last the test of time and have readers fascinated by, that needs to be your focus. The actual events that transpire in your novel are largely irrelevant, or at best interchangeable, they exist only to serve the growth of that character. Everything they do, and everything that happens to them, needs to be strictly relevant to character growth, or at least have a nod to it. You may have your heart set on a specific set of events for your character, but what if there's a more relevant set of events out there that would better serve yours and your character's needs, shouldn't you be receptive to them?
If you intend to write a sequel or another book in the series, that should be a key focus in your writing throughout. How much you allow the reader to know about the characters, how many loose threads you leave dangling for picking up in subsequent books. If your storyline revolves around a specific event that would make sequels difficult, consider abandoning the event, even if it means a complete re-write of your story.
Planning isn't just about setting out a timeline of events for your book. It's about thinking hard about what you hope to achieve. Work out why you're telling this story, where you intend to take it, will the story or its characters last beyond this particular book? If you want your reader to feel sad, nudge them in that direction, if you want them to feel hope give them something to cling onto. It's surprisingly easy to tell when an author has these things in mind, easier still to tell when they don't.