The Default storage in GB setting controls the default allocation for new OneDrive for Business sites. It has no impact on existing sites. Though the actual size of your OneDrive for Business site can be expanded (depending on your subscription), the maximum initial size is 5 TB. The default is 1 TB. If you assign a default size larger than a user is licensed for, their site will be rounded down to their licensed amount. The minimum size you can configure is 1 GB.

You can also use PowerShell to manage the initial storage setting. Connect to SharePoint Online with the SharePoint Online Management Shell, and then run the following PowerShell command: 

Set-SPOTenant -OneDriveStorageQuota <Size in MB>

Now that you know how to allocate storage space, let's look at managing data after a user account has been removed.