Quote:The developers of VeraCrypt introduced Personal Iterations Multiplier (PIM) functionality in the encryption program in version 1.12.

Quote:PIM stands for "Personal Iterations Multiplier". It is a parameter that was introduced in VeraCrypt 1.12 and whose value controls the number of iterations used by the header key derivation function.

PIM is used by volumes even if the creator of the volume did not specify a value. It is an optional component that improves security: it adds another step to the authentication process similarly to two-factor authentication. The main difference is that the PIM value is fixed and not generated on the fly when requested. An attacker needs to know the master password and the PIM, if not set to default, to breach the encryption successfully and access the content of the drive or partition.

A couple of good reasons exist to change the PIM value:

• It was leaked or stolen.
  
• The default value is used and that is not as secure as using a custom PIM.
  
• You want to change the PIM to speed up or slow down the boot process.
  

Full reading: https://www.ghacks.net/2018/11/26/how-to-change-the-pim-of-a-veracrypt-volume/