It is typically used to update a master list with transactional items, and includes options to ignore empty update fields and to only update a field if it is empty.
Update from Table – select a worksheet or previously named table from the drop down list. The worksheet must be in the same workbook, and data must start in cell A1 with a header row. If you want to use a table in memory, use Table Name to create the reference.
Select Key Columns – select columns that will be used to align the two tables together. All values from all selected columns must match for a row to match.
Ignore case – when performing the comparison, match rows even if they have differing upper or lower case letters.
Ignore spaces – when performing the comparison, match rows even if they differ because of different spacing (leading, trailing or within the text).
Replace only empty cells – do not update existing values unless they are empty.
Ignore update if empty – if the reference table contains empty cells, do not modify the matching row in the current table.
Add new columns – add any columns from the reference table that do not exist in the current table.
Add new rows – add rows from the reference table with values in the key columns that only exist there.
Blog article: Using the Update Function