Prozac has a notoriously long half-life, which is one of the reasons it's indicated for adolescents who are likely to skip/forget doses.

The long half-life is also the reason it's prescribed for SSRI withdrawal symptoms.

Sertraline is a potent SSRI in terms of inhibiting the serotonin transporter protein itself. It also has a relatively short half-life. Makes sense that cessation would induce withdrawal symptoms.

It's the same principle behind prescribing Suboxone for opioid withdrawal. The drug has a ridiculously long half-life, so it has the potential to smooth out what would otherwise be acute withdrawal.