The Magnesium makes you poop because the Magnesium Citrate helps to relax your digestive tract muscles.
Aside from relaxing your digestive tract muscles the Magnesium also helps to neutralize your bodies stomach acid which also helps your poop flow freely.
If you're constipated or just having trouble with pooping when needed then taking some magnesium at night before bed can help get your bowels moving.
You should also take magnesium supplements daily if your magnesium levels are low because having the proper level of magnesium is needed to stay healthy and to keep your bowels moving.
Some other benefits of magnesium are that is helps to lower blood pressure, has Anti-Inflammatory properties, protects against diabetes and also helps reduce insulin resistance and helps with depression.