This summary is not the rule. The rule text controls.
If someone is charged with multiple crimes in separate cases, or if several people are charged in connection with the same events, the court can combine these cases into one trial. This is allowed as long as the charges and defendants could have legally been listed together in a single set of charges from the start.
If the cases do not meet that standard, the court can still combine them for trial, but only if the people who are charged agree to it. This option exists mainly to make things easier and more efficient, such as saving time or avoiding repeat testimony from the same witnesses.
For anyone facing charges, this means your case could be tried alongside another case if the charges are connected or if you agree to combine them. This can affect how your defense is prepared, since evidence from more than one case may be presented to the same jury at the same time.