Question: For some reason I feel its overkilling on the use of article(the) here, 

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> To refine the results, please use the categories on the left
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Can someone help?

Answer: 
As a native speaker, I can definitely say 'the' is not overused in this sentence. The is one of the most common words in the English language, so often in fact you might use the word 'the' over 5,000 times *in one day.*
@shin is correct, the sentence is fine. **To refine results, please use categories on the left.** is equivalent, but the difference is stylistic.