The Lerp solution works well for this one animation for this one box.
But what if your graphic designers get the idea to replace the box with one which has a more fancy opening animation with far more moving parts?
Doing that as an animation in the 3d modeling program might be far easier than animating all the sub-models with scripts. It also allows to simply replace the 3d model with a differently animated one in a simple drag-and-drop manner without having to change any code.
But when you don't plan to have such complex animations in your game, then using the animation system might be overkill.