In addition to notes in other comments, vertical slicing helps to avoid a tendency for rigid layers to emerge (think the rigid and doomed-to-be-messy Controller -> Service -> Repository "pattern"), which ultimately helps lead to looser, more naturally composed component structures.

You can still have files and folders that cut horizontally across those modules (e.g. for things like logging, sending an email, etc. etc.) - in fact, organizing your hierarchy in vertical slices helps to _promote_ good isolation of those cross-cutting concerns.