Too many repetitions of the same word in a short space, such as within a single paragraph or even withing a single sentence, can be distracting to your readers and throw off the flow of your prose. Take a look at the following example:
The wall was too tall to climb, but only just; it was short enough to seem climbable but tall enough that a fall from anywhere near the top would kill you. Raek studied the wall carefully and realized that the top of the wall was covered in a slimy-looking green moss that would make climbing impossible. But if he couldn't climb it, how would he get over the wall? The wall was between him and the chalice. He had to get past the wall.
Notice how the words "the wall" get repeated over and over again? Six times in one paragraph. Some variation of the word "climb" appears four times as well. It feels awkward and clunky. Cleaned up, that paragraph might look like this:
The wall was too tall to climb, but only just: it was short enough to seem scalable but tall enough that a fall from anywhere near the top would kill you. Raek studied the wall carefully and realized that the top was covered in a slimy-looking green moss that would ensure that anyone clinging to the rock would lose their grip. But if he couldn't climb the wall, how would he get over? It was between him and the chalice; he had to get past.
This version is smoother, with just three uses of "the wall" and two of "climb." Some of the repeated words were replaced with synonyms ("scalable" in place of "climbable"), some were removed by heavily re-writing the sentence, and others were simply not necessary to begin with and could be removed without changing anything else.
Now, sometimes repetition can be used to great emotional and poetic effect; but unless you're very confident in your use of it, you should avoid it as much as possible.
This is one of the reasons I recommended that you avoid dialog tags as much as possible in this post. Dialog tags can get overly repetitive very quickly.