That depends on how you class "for free". Most people think free = not being paid money.

I'm actually looking into working for the whole of July for no monetary compensation. But in return, I expect to learn something from whoever I work with/for.

Most of the time money is good. You can exchange that for many things in life. But sometimes, knowledge is better to have as you can exchange that for (even more) money.

And from an employer point of view, you should not be judged by the size of your pay cheque, but by how much value you actually add to a company.