ValueRenderOption

Determines how values should be rendered in the output.

Enums
FORMATTED_VALUE Values will be calculated & formatted in the response according to the cell's formatting. Formatting is based on the spreadsheet's locale, not the requesting user's locale. For example, if A1 is 1.23 and A2 is =A1 and formatted as currency, then A2 would return "$1.23".
UNFORMATTED_VALUE Values will be calculated, but not formatted in the reply. For example, if A1 is 1.23 and A2 is =A1 and formatted as currency, then A2 would return the number 1.23.
FORMULA

Values will not be calculated. The reply will include the formulas. For example, if A1 is 1.23 and A2 is =A1 and formatted as currency, then A2 would return "=A1".

Sheets treats date and time values as decimal values. This lets you perform arithmetic on them in formulas. For more information on interpreting date and time values, see About date & time values.