If we compare this feature with other programming languages, then, for example, in C# you can separate the implementation of classes in several files and you can declare references to any public classes and any internal classes in the assembly, regardless of in which files the class is declared.
Perhaps in Delphi we need to introduce such a concept as an assembly or library, within which classes can refer to each other in the interface part.
In general, when developing classes, you want to operate only with such concepts as a library and a class, but you don’t want to think about which file it should be described in so that it can be used in other classes of the library.