from what i've experienced, it is a mild detox technique, but it also stimulates circulation to the head which is a good thing, but I do agree if the body is working correctly we shouldn't need to do it for toxin elimination, but it can be an aid when other things are clogged up, or part of a healthy routine since you have said so many times its hard to be clean in the world today, so adding another route to get rid of stuff isn't too bad. also the dental effects are nice too.
what I really enjoy is a good abyanga oil massage, where I first do a 10 minute skin brush of the whole body, then some light stretching and warm up, then massage the body towards the heart with an unrefined oil all over the body, let it sit for 15 minutes and shower off. I get a good detox reaction from this dumping the congested lymph into the blood and then filtered out by my kidneys, and occasional skin breakouts since i'm so toxic. BUT nothing can replace a clean diet! the most important thing of all.