Google Backup and Sync super slow and 100% CPU usage for days
I thought it would be more efficient to leave it on but I noticed that the number of files synced was increasing more slowly as time went on. Possibly due to an inefficiency as the back app was continuously scanning unsynced files. After a few days it was managing just 1000 files a day. When I restarted it would manage 500+ in the first half an hour.

Rather than constantly restarting the app here is an Apple Script which helped speed things up. It restarts Google Backup and Sync every half an hours which really helped.

Open the apple Script Editor. Copy the text into the script editor and hit “Run"

repeat
    log "About to start Google backup and sync"
    tell application "Backup and Sync" to activate
    log "Starting for 30 minutes..."
    delay 1800
    log "About to quit Google backup and sync"
    tell application "Backup and Sync" to quit
    log "Application Closed"
    delay 60
end repeat