nested set model sorting

yo,

on this page What are the Options for Storing Hierarchical Data in a Relational Database? there is an awesome comparison of options for storing hierarchies. For me it looks like nested set is the best, but there it mentions "Requires a specific sort order". Can anybody explain what exactly does that imply? Will I be able to get a sorted list of ascendants/descendants fast only I sort them by id? Even if I have indexes on other columns that I'm trying to use for sort?