Students who understand sight words can have higher fluency levels when it comes to reading because the reading can go much more quickly. When students don't have to sound out each word, and can instead look at a word and know what it means, they are able to move onto the next word without stopping. This doesn't interrupt the reading flow and students are able to understand more about the reading process; therefore, students who know more sight words usually have better fluency -- they don't need to stop while reading, and can continue on with the sentence.
Higher Reading Levels
Students who know more words by sight might be able to read at a higher level than their peers. If peers are struggling to sound out each word as it comes, they might be reading at grade level. But if students can look at words and know what they mean, they may actually be able to read higher-level material.
Higher Reading Speed
Along with fluency and reading levels, students who know more sight words can also read faster. A lot of this has to do with the fact that they do not need to stop and sound out words. It also has to do with the fact that as they get better at sight words, they can often look at entire sentences and know what they mean instead of reading each word. This makes reading faster.
Students who know more sight words and can recognize them can often understand passages they read better than students who are sounding out all of the words. This is because students already know the meanings of all of the sight words they are seeing, so they are able to understand the entire passage much quicker than otherwise.