We had an event where a field used in a custom form that was being used for project log was modified resulted in loss of data within the field for 8300+ log items. This was a massive data loss for Logs from the past 3 years and is typically where work comes from for our site.
Another Field was completely deleted resulting in the same issue.
It would be very helpful to give a way to move data from the sandbox to the production system easily. Another way to help mitigate this is to put deleted fields into the recycling bin for possible restoration.