Check data integrity
From LimeSurvey Manual
The Check data integrity function checks the consistency and the redundancy of data. It can be accessed from the Configuration dialog:
Data consistency check
It looks for possible errors that might exist between the response tables and survey tables or between the token list and the CPDB, and so on.
For everything to be alright, all the values from the screenshot need to meet the consistency standards.
Data redundancy check
If you deactivate a survey, the token tables, the response tables etc., will not be automatically deleted. They will get stored in archived tables. If you do not need them anymore, use the Check data integrity function and select the "leftovers" you wish to delete: