Hi Habit,
The Order in Layer refers to the rendering order. If it’s just about sprites, not about colliders, using the Order in Layer is perfectly fine to solve your problem. 
If you have a complex game consisting of a foreground and background sorting layers could make sense to quickly define in which general order the sprites are supposed to get rendered, for example, sprites of the foreground should always get rendered after sprites of the background.
Please feel free to toy around with this feature to learn what it can do for you.
See also:
- Forum User Guides : How to mark a topic as solved