SharePoint is fairly good at sharing files: it allows upload by drag and drop, it supports versioning and approval of documents with a decent user interface, it offers a reasonable organization of users and permissions. Running SharePoint is anything but trivial, but with some discipline it can actually solve problems for end users.
For external people likely not, usually Sharepoint would be behind some VPN and Firewall. Some cloud service like Dropbox might work if allowed (which it often isn't). And then there will often be the resulting sprawl of various services: this for secret internal stuff, that for external people, yet another thing for marketing, etc.
The problem with using sharepoint is that now you have sharepoint, and people will start using it, with all attendant horrors.