Store your file in OneDrive for Business. Documents you place in OneDrive for Business are private by default, unless you place them in the Shared with Everyone folder. This makes OneDrive for Business your best option for draft documents or personal documents that no one else needs to see..
What type of sharing are you planning on?
Wide sharing scope or a longer lifecycle. individually and with a limited scope or lifecycle.
Store your file in OneDrive for Business. For example, you’re writing a blog post that may not be associated with a project, and you’d like a few colleagues to review it before you post it. In this case, you expect people to use the document once without needing additional storage or context information. All they need is a link to the document and editing permission..
Is there already a SharePoint site or Office 365 Group for this type of document?
Use the existing storage solution. Talk to the owner of that solution if you feel it should be moved or migrated to another source..
Do you need granular permission levels or check-in / approval workflows?