A simple rotation of the sandbag (or kettlebell, if no sandbag is available) while descending into a reverse lunge will challenge your strength and core stability in the transverse plane.
When you add in the power of a swing, what you wind up with is a really cool explosive movement – the swing requires decelerating the implement at the bottom of the movement before you explode from the lead leg into hip and knee extension.
A perfect warm-up virtually ensures a perfect workout, but a poor one will almost certainly ruin what COULD have been a great training experience. Ever wake up dreading the idea of going to the gym, but after getting there, you end up having a great workout? You can thank your warm-up for that.