It may be helpful to understand how your quota is calculated. Metadata (thumbnails, temporary files, cache) takes up about 10% of disk space, but is not counted against user quotas. Some apps store information in the database, such as the Calendar and Contacts apps. This data is excluded from your quota.
When other users share files with you, the shared files count against the original share owner’s quota. When you share a folder and allow other users or groups to upload files to it, all uploaded and edited files count against your quota. When you re-share files shared with you, the re-share still counts against the quota of the original share owner.
When version control is enabled, the older file versions are not counted against quotas. If you create a public share via URL, and allow uploads, any uploaded files count against your quota.