User-story maps help Agile teams define what to build and maintain visibility for how it all fits together. They enable user-centered conversations, collaboration, and feature prioritization to align and guide iterative product development.
It’s never about writing better requirements; it’s all about fostering collaboration. Read more about it in this article: https://medium.com/serious-scrum/what-not-to-do-with-user-stories-be38ddc76df9
You can use storytelling to explain why slicing work is important. An colleague Rene de Leijer shared me the following story:
You are on holiday in the USA and driving already for hours on route 66 from the Grand Canyon to Las Vegas. Your stomach is roaring and your eyes are looking for a real American hamburger (sorry for the vegans). You see yourself eating one with both hands holding it in front of your mouth. And finally, in a small village, you see a strange burger cottage. Do you want to eat something in that weird place or keep on searching for another place to eat? But maybe that will take an extra hour. So yes you decide to stop and ease your hunger. The sign on the door says “Pull”, so you pull the door and it does not open. “Whahahaha” you hear someone laugh. You really feel weird on this and get a little but irritated, being hungry is not helping on this. You order a huge burger and the man behind the bar says “I will get you something in a minute, sir”. After 1 minute he puts a delicious piece of bread on a napkin and asks if you need some ketchup on your burger. And after my confirmation, he put some ketchup on the bread. After 3 minutes he puts an incredibly tasty burger on the bread, you really smell it and are eager to take a bite. “Sorry the burger is not finished yet” he says and my stomach is roaring all the time, while I am staring at that delicious piece of meat. 1 minute later, he puts some lettuce on top of the burger and only 2 minutes later some extra ketchup. “We are almost there sir” I hear him say. And finally, some onions and the last piece of bread are adding on top of it. “Well sir, now you can eat your burger, we have done everything in our power to give you the best burger you have ever tasted”. I pick up the burger and take a huge bite, and I spit it out, the bread is soggy, the burger cold and my hunger is vanished . How would you feel if you are this person, I think very disappointedly and he is leaving to find some other food? And do you see a comparison with our way of developing? Do you think the customer would enjoy if we deliver him every 2 minutes a small slice (top-down) of the burger ?