Routing templates thats start with an underscore
Yes, prefixing a template's filename with an underscore does what it says on the box – any underscored template will be excluded from route mapping.

A typical use case is to use underscores for partials or wrappers, e.g. "_mainmenu.html" or "_baseTemplate.html" – essentially any template that doesn't make any sense to load up or access directly in the browser via that template's path.

This isn't a mandatory thing, but a good practice.