Storing cryptsetup headers separately has some advantages, firstly, without them, the block device itself is a set of Entropy, from which it is impossible to determine the type of partition / encryption / device.
Secondly, it is a small file that can be easily backed up without using dd.

Simple cheat sheet

Generate a password.

1

cat /dev/urandom | tr -dc '[[:print:]]' | fold -w 256 | sed 's/ //g' | fold -w128 | head -n 1