Minor correction - the penalty pay is not guaranteed. The employee is free to request it, but the DLSE will decide whether or not to grant it, and they are far more likely to do so if the employee has attempted to work out the issues with the employer.
Direct from the DLSE website (emphasis mine)
An employer who willfully fails to pay any wages due a terminated employee (discharge or quit) in the prescribed time frame may be assessed a waiting time penalty. The waiting time penalty is an amount equal to the employee's daily rate of pay for each day the wages remain unpaid, up to a maximum of thirty (30) calendar days. Mamika v. Barca (1998) 68 Cal.App4th 487 An employee will not be awarded waiting time penalties if he or she avoids or refuses to receive payment of the wages due. If a good faith dispute exists concerning the amount of the wages due, no waiting time penalties would be imposed. A "good faith dispute" that any wages are due occurs when an employer presents a defense, based in law or fact which, if successful, would preclude any recovery on the part of the employee. The fact that a defense is ultimately unsuccessful will not preclude a finding that a good faith dispute did exist. However, a defense that is unsupported by any evidence, is unreasonable, or is presented in bad faith, will preclude a finding of a "good faith dispute". Labor Code Section 203 and Title 8, California Code of Regulations, Section 13520
Notice that it says the penalty wages MAY be assessed, not WILL be assessed.