Usually, when we come across an unknown word, we can guess its meaning based on the text around it (assuming that all the words around are known). However, there are cases that the meaning of the word is crucial, and only guessing it is not enough. We have to look it up in a dictionary.
Do we have an advantage if we know the word beforehand? If we can understand the text by just looking up the unknown words, then I guess there is no reason to keep learning vocabulary, right? I feel that learning vocabulary ahead is important, but I don't have a solid reason to back it up. My main purpose in learning English is to "understand what the world says", and as long as I can understand it with the help of dictionaries when coming across a new word, then the reason to expand my vocabulary to reading is mitigated.
One possible advantage of learning vocabulary I can think of is that because we don't have to pause reading to check the dictionary for the definition of the word, the reading comprehension will be maintained. Getting interrupted reduces productivity. But the time taken to check the meaning can vary. In digital devices, you can check a word's meaning in only a couple of seconds, hence it doesn't take much time to understand the word before continuing your reading flow.
Note that I'm only interested in the reasons for expanding vocabulary from a reading point of view. I know that it will also improve my writing skills significantly, but that's another story. I'm also only interested in the looking up word action, not guessing its meaning.