It depends on the industry and company norms. Certainly the job of creating advertising/PR is to sell products, but you also don't want to create anything that states (or implies) qualities that your product doesn't have, or makes subjective claims that different people may interpret differently. Certain words - even words that seem to be common usage - carry implications and restrictions. Eg. for how long can you claim a new product is "new", what do you have to do to say it's "improved", what is "low fat" vs. "non fat" vs "light"...
I'm not familiar enough with tech marketing or your product to say why specifically you can't say the words you mention, but I suspect this is the reason why. So - how powerful is powerful? As powerful as a AAA battery? It's efficient? Based on what scale? How do you know it's efficient? Etc.
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