My tolerance for multiple classes in a file or larger classes is heavily driven by what tooling I have available. If I've got a structural outline panel, like

My tolerance for multiple classes in a file or larger classes is heavily driven by what tooling I have available. If I've got a structural outline panel, like in IntelliJ-based editors, or the SuperCharger plugin in Visual Studio, then whatever, it's easy, because I have that table-of-contents to easily navigate with. With less powerful tools, the "every type in its own named file" pattern is much more useful.