iCloud and deleting files in Mobile documents

Can I delete these to free up space? Thanks

No, if you delete them, you cannot access your iCloud Drive. That folder is where iCloud Drive is stored on your Mac.

Storing on iCloud Drive will not free space on your Mac. It is not an external drive, it is essentially a synced folder. iCloud Drive keeps the documents on your Mac in sync with iCloud and across all other synced devices.

Yes, the drive is mainly for syncing. See this link: iCloud Drive FAQ

Here's what you can do with iCloud Drive:

• Store and access all of your documents in one place from any of your devices
• Keep files and folders up to date across all your devices
• Create new files and folders from iCloud-enabled apps
• Work on the same file across multiple apps

To free space on your Macs internal drive, get yourself an external drive. The new portable SSD drives are so small, that it is no hardship to carry them around.

So, if I want to free space I need to save files on external hard drives, iCloud simply enables me to effectively view files across Apple devices.