The link that Paul put up really makes this pretty clear, the jury is out as to whether or not this has any real benefit, as the study of it was flawed in design.

As you can see from the recurrence forum, it does happen to some people. Why, no one knows for sure. Obviously it is some combination of their specific etiology and their genetic make up. But it is highly unpredictable who will walk this path and who will not. If the cause is indeed a function of their etiology and genes, then the chemo wash at the end, when there is no known disease remaining, does not make sense. I have heard that argument from several oncologists. If there is a risk, because of the advanced stage of the first cancer when found - that there might be some small undetectable by any technology scans that we have, micro metastasis, then you could make an argument for it.

Remember that there is a difference between local recurrences, and second primaries, which are known to occur elsewhere in the body as a result of the first. IMO if you have been declared free of disease after primary treatment (NED) then adding more to the mix is certainly counter intuitive. There isn't anything there to go kill.

The original idea was that in people that have recurrences, that there must be some residual, but undetectable diseased cells remaining, that after a couple years finally prosper and spread enough to be discovered. Actually this would not be technically a recurrence, just incomplete primary treatment. It used to be a problem several years ago when people had surgical only solutions for smaller tumor sites and did not have chemo radiation at the same time. Field carcinogenisis which takes place in many oral cancers, yields a primary timor that isn't always very focal. there are cells surrounding it that look normal (to the surgeon) and are outside what a normal surgical margin of X centimeters might be, but at the individual cell level have already developed aberrations in themselves to become low grade or even high grade dysplasia, the second of which is the stopping stone to full malignancy.

There historically has been a push to use this unproven idea in younger, stronger patients who could tolerate it better as well, "just in case".

Now with money so tight, and budgets at NCI and elsewhere being cut, a clinical trial which would find out definitively if this is something that works or not likely isn't going to be done in the near future unless some oncology chemo company wants to pay for it, for business reasons.

Bottom line, there is no good answer here. Flawed trials to argue for it, unknown real benefit from peer reviewed publication vs. anecdotal clinical experience and some hospitals and doctors advocating for it with in their opinion some measurable results. ( I don't know how you measure a non recurrence as existing because it just didn't happen biologically, or because you gave someone more chemo - either way it didn't happen). If a recurrence happened and you didn't do it, there would be a normal human desire to say we should have. But that is not a science based idea. You could do this, and if the cause is not residual micro disease, it would make no difference at all that you did. There recurrence might happen anyway from whatever genetic/immune system aberration allowed the first to happen.

Temper all this with the fact that while the least damaging of the treatments, chemo is not without life long morbidity issues. Peripheral neuropathy for one.