I am tired of being called a double dipper. This is a myth perpetuated by either people who are ignorant of the facts or want to stick it to the taxpayers for every dime they can get.
The retirement pay does not come from the taxpayer. The retirement fund is money collected from employees and employers as part of the employee's pay while working full time. The money is invested.
Retiring and coming back to work part time is one way of gradually phasing out of the job. People who have worked for 20 or 30 years on a job and suddenly stop find it a real shock. Some die within a year of retirement. A person should retire to something, not from something. Returning to work part time is one way to do that.
In addition it is an advantage to the employer. The person is already oriented to the job, knows where things are and has a working relationship with the other employees.
In my case I was able to tell the person who replaced me where connections were, the use of some of the unfamiliar equipment and familiarize him with some of the procedures. I also finished a deadline grant project.
Another benefit to the employer is that they do not have to pay some of the benefits, the most expensive being health insurance.
I read about a factory in England that has a special shop for retirees. They may come and go as they please and work on whatever they want. Over the years some of them have developed items that have benefited the company.