This summary is not the rule. The rule text controls.
When people are accused of working together on a crime, or on a series of related crimes, prosecutors can charge them all in the same court document instead of filing separate cases for each person. This applies when the charges come from the same event or from connected events that are part of the same criminal activity.
The rule also gives prosecutors flexibility in how they write up the charges. They can list all the defendants together under one count, or they can break the charges into separate counts. Not every defendant has to be named in every count. For example, if three people are involved in a crime spree, one person might be charged in all the counts while another is only charged in one or two, depending on what each person actually did.
This approach saves time and resources by letting one case cover multiple people instead of running separate trials for each defendant. It also lets the court see the full picture of how the alleged crimes connect to each other.