Punch Code is used by the employee to punch ENTRY, EXIT, MEAL and BREAK.
Payroll Code is used when sending information to payroll that represents the employee.
These numbers are typically the same but, in some cases, may be different.
If your payroll code is longer or contains alpha values and you want to keep a simple numeric code, this would be the right usage for it.
For those of you who change ownership, you can keep the employee codes the same and just change your payroll code.