In Altium Designer, the thick red line separating each circuit is called "dividing line", which is usually located at the edge of the schematic diagram and is used to divide the circuit into multiple logic units, which is convenient for management and maintenance. Delimiters can be defined by "location". Delimiter "command, or you can draw a rectangular box manually and convert it into a delimiter through the right-click menu.

The main reason for using separators in schematic diagrams is to improve the readability and manageability of circuits. Using separators, the circuit can be divided into multiple logic units, such as control unit, data processing unit, power supply unit, etc. Each unit has its own function and is independent of other units. This can make the whole circuit structure clearer and easy to maintain and modify.

In addition, the use of separators can also facilitate the version control of the circuit. Since each logical unit is separated by a separator, each unit can be modified independently without affecting other units. In this way, version control can be carried out conveniently, because a small error needs to redesign the whole circuit.

In a word, the use of separators in Altium Designer can improve the readability, manageability and version control ability of circuits, so it is recommended to use separators to divide logical units when designing large-scale circuits.