In most cases, the trigger owner is also the owner of the table (or view) on which the trigger is based. In those cases, the table owner, with CREATE TRIGGER can create create triggers on their own table.
CREATE ANY TRIGGER allows the user to create a trigger owned by any user on any table. It is a big security hole because they can create a trigger owned by a privileged user on a table that they own or can insert into. Because they can insert into that table, they can force the trigger to execute and the trigger executes with the privileges of the trigger owner. The effect is that a user with CREATE ANY TRIGGER privilege can create and execute code as a privileged user (similar to having CREATE ANY PROCEDURE plus EXECUTE ANY PROCEDURE).
Limit to as few as people as possible and audit appropriately.