In terms of backing up your data there is one important restriction:
Only the first 2.500 characters of text fields & comments are backed up.
Regarding the syncing of your backup to Google sheets, there are two additional restrictions:
A Google Sheet cannot have more than 2 million cells (i.e. fields * records)
If an app has more than 50K records, there will be no Google sheet created. However the data will still be backed up on our AWS servers.
When a Google sheet exceeds the limit of 1.5M cells, a new Google sheet is created with fewer fields. The previous version of the Google Sheet will be moved to the Archive folder. In this case you will still see all records, but not all fields will be shown in the Google Sheet (we always backup all fields on our Amazon cloud servers)
A cell in a Google Sheet cannot contain more than 4.000 characters. If a text field (e.g. a comment) has more than 2.500 we will only back up sync the first 4.000 characters.