- What is the impact of not storing my documents on SharePoint?
The main thing to think about is the size of the database, as you store and link more documents in Microsoft Dynamics 365 Business Central the more it will grow regarding achieving your documents. Its not recommend for businesses who plan on storing and retaining a lot of documents.
- Can you drag and drop directly from Outlook?
The following 'free to use' add-in for Outlook enables you to drag direct from your Outlook inbox and creates a .msg file just as if you have gone via the desktop. Admittedly having to install a setup.exe client side is not perfect but then they are using client-side software with Outlook so that's an Office problem not a Dynamics problem. https://tonyfederer.github.io/OutlookFileDrag/
To use just download the 64bit version, run the setup.exe then restart outlook and it should ask you to authorise the drag and drop add-in.