Containers might not be necessary, but learning about them in an easy game is better than not knowing about them when trying to create something harder.
When working with a hitbox and seperate sprite for the enemy it is easier when the sprite and hitbox are "connected" so when you destroy or hit one the other one is automatically "linked", it makes the picking part, which many construct2 users confused, a little easier.
Here's the manual entry on containers
If you put the enemy sprite and the hitbox together in a container, when you say on collision with hitbox, enemy play death animation, only the "linked" enemy will play that animation.