Word Frequency Counter
Overly using the same word in writing can become repetitive and produce boring results. It can also draws attention to itself and tends to standout by looking unusual. English is a rich language and when we overly repeat words it can look lazy, careless and not to be in full command of the details of your work.
Of course it is expected that utilitarian words like "the" are going to be use frequently without anyone noticing. But as a general rule avoid repeating words with in a paragraph, and definitely within the same sentence.