CLUSTER using sequential scan followed by sorting I'm tring to understand the meaning of the following clause from PostgreSQL 12 docs


  CLUSTER can re-sort the table using either an index scan on the
  specified index, or (if the index is a b-tree) a sequential scan
  followed by sorting.
  
  When a sequential scan and sort is used, a temporary sort file is also
  created, so that the peak temporary space requirement is as much as
  double the table size, plus the index sizes. ... you can disable this choice by temporarily setting
  enable_sort to off.


Clustering is meant to physically reoder the table based on the index information. So what is going to happen if I set enable_sort=off? Will it still manage to reoder the data properly? If yes, then what is the benifit of having the enable_sort option in the play here at all?
TFM says: 


  It is impossible to suppress explicit sorts entirely, but turning this variable off discourages the planner from using one if there are other methods available.


So yes, it will reorder the table rows properly, but will try to chose an alternative, potentially slower, access method, if at all possible.