I see people raising this argument almost always only when they want to continue a practice that has no provable benefit, and often one which is patently dangerous.
However, what science does do is to say that if something is disproved, you can't keep latching back onto it. Astrology is an example of something that's been completely disproved, both by increasing knowledge of how astronomical bodies work, and by empirical means. Another is homeopathy, which has been disproved in exactly the same way. At this point, it's time to put these to rest.
Things unproved would include the efficacy of certain Ayurvedic and other traditional medicines (though others are disproved, like rhino horn preparations in traditional Chinese medicine), or, well, the existence of god (though there are certain atheists...)
T.R. Shashwath I had seen enough Ayurveda in my life and we never went to English doctor until our family ayurvedic doctor (Tarakaturi Achari of Machilipatnam) passed away at the age of more than 100. His hospital was always filled with patients and he would cure many diseases that would otherwise take a very long time to cure if not not cured by allopathy at all. He was treating dreadful deseases like cancer, brain tumour etc., with ease. Just one small pill a day is enough for a diabetic person to eat as he likes like a normal being. Tonsils would disappear forever in a week's time. Now how do we make such Ayurveda to be *scientifically* proven?. Subject those drugs to lab tests and come out with the results?. In deed, do we need to?
I still remember UK terming Yoga as as unscientific sometime back. Now it is a world-wide phenomenon. Unfortunately Ayurveda is dying with people like Tarakaturi Achari. Soon it will disappear and remain as one of the superstitions.
The test that stands ahead of any test is the 'time test'. Practices like Ayurveda, Yoga etc., were followed for many centuries with 'proven' results. It is good to be proven by modern science, but not must, just like mechanics of quantum particles cannot be proven by Newton’s laws of motion. Hence I appreciated Aparna Krishnan's post earlier.