Editing a group opens the container to allow you to make changes. When you exit the edit mode the container gets closed up again. Explode takes the container off of the group and throws it away. It generally doesn't make sense to explode a group to make changes to it.
If you explode a component to make changes to it, the geometry will no longer be related to the other instances of the component in the model so those other instances will not get the same modifications. If you want to make changes to an instance of a component without changing the others, it is better to use Make Unique before editing. Don't explode it.