Named selections and sets seem to be identical but, in fact, both are designed for different purposes:
- A named selection is fixed, while a set is flexible and can be modified.
- You can perform operations between sets, while you can't with named selections.
- Named selections keep the current order of records, while sets do not.

So, if you need to work at the record level, checking if a record is a member of a specific selection, you would most likely need to use sets, which are very fast in 4D.

If comparing selections is not an issue but you just need to keep an ordered selection, you may, in that case, use named selections.