When you install mods, they are kept in an ordered sequence. As soon as you run the game, it will load its main files and mods by following that sequence. If there is something wrong with the load order, the game can get unstable and crash.

To keep your game stable and avoid crashes, the load order of your mods should have no problems.

You can change the load order of your mods manually, but it is much more practical to use a tool that can automatically do that for you. So, LOOT comes to help you a great deal with that.