All it does is change the way the list is displayed, it doesn't affect your data at all.
Helps if you understand the whys and wherefores. Remember that when you have a "many" relationship in a relational database, where the 'parent' table can have multiple 'child' rows in the related table, and you select that parent using a 'join' to the child, like this ...
SELECT * FROM parent LEFT JOIN child ON parent.id = child.parent_id
... if you have (say) three rows in 'child' which all have the same 'parent' (in Fabrik terms, you have 3 repeats of that child group), then you get back three rows from the select. The rows in the selection will share the same parent row data, but have different child data, like ...
parent.id, parent.moms_name, parent.dads_name, child.id, child.childs_name
1,Jane Smith, John Smith, 1, Little Bobbie Smith
1,Jane Smith, John Smith, 2, Mary Jo Smith
1,Jane Smith, John Smith, 3, Chuck Smith
So ... how should that be handled when it comes to displaying your data in a List?
If you have "Individual rows" selected in your join settings, the above is what your list will look like. Three seperate rows, one for each "repeat" in the result set, with the data from the 'parent' repeated.
If you select "merge", then we'll take that repeated data, and reduce it down to a single row, with the repeated data shoe-horned in to a single table cell for each column ...
Code:
1, Jane Smith, John Smith, 1, Little Bobbie
2, Mary Joe Smith
3, Chuck Smith
It's safe to play with - like I said, it doesn't change anything except how the list is displayed, nothing is changed in your data.
-- hugh