OneDrive and OneDrive for Business are two different Products, but due to its similar name we get confuse at times that what is what?
OneDrive is the Online File Share which user gets with personal email address with Microsoft, like Hotmail.com or msn.com and you get 5GB of space for free.
OneDrive for Business is the File Share that user gets with the business email address when the person logs in using Company email address and password. The Organisation gives employee the email id with the company domain name, and then user can have this product as part of the Office 365 subscription. This is a Premium Subscription and User gets upto 1TB of storage or 5TB depending on the Subscription you have. Subscription Link : https://products.office.com/en-au/onedrive-for-business/compare-onedrive-for-business-plans
You can get upto 1TB of storage in One Drive for Business, can use it as a File Share, and Share the documents with employees and external stakeholders.
For external users, the SharePoint Online Administrator needs to allow sharing at the top level by adding the external company’s domain name in the list so that users can share documents with the external users.
Lets take an example: Suppose I am working with a vendor called ABC and I have to share some documents with my vendor Adam, whose email id is email@example.com then I will allow abc.com domain on my “SharePoint Admin Center” in the “sharing” tab to allow sharing of the documents using OnDrive for Business with vendor in ABC Company.
OneDrive for Business is a useful Product & rather using SharePoint for storing and sharing heavy documents, users can store their documents in OneDrive for Business and implement a complete life cycle by deploying workflows and alerts.