Guido, I think the tangible benefit is that we, as measurers, make money from our USATF affiliation. If USATF didn't have the certification program, we would not have our hobby-job.
USATF membership may be likened to an older couple (I can say that, I are one!) paying property taxes on their home, some of which goes to schools. They have no one in the school system, but they indirectly benefit from the education of others' kids.
Sure not saying measurers must, but we benefit from the existence of USATF. I think that should be seen as a "professional membership", to put it in IRS parlance.