I came across this thread on Facebook where a Logos Bible Software user was querying the usefulness of original language study. This response was so good, I wanted to keep it for future reference.
Q. What are the benefits of learning biblical Hebrew and Greek?
A.
1. You are not relying upon the interpretation of others. ALL translation involves at least some interpretation. By knowing the original language, you can see and better understand the decisions made by English translators. (Just to be clear, most English translations are great and faithful to the original, but they have different philosophies of translation and always require interpretation of context.)
2. You will see additional nuance in the text. The phrase "lost in translation" exists for a reason. Sometimes you notice things in the original languages that aren't so apparent in English translations. For example, in both Hebrew and English word order can be used for emphasis within a sentence in ways that don't work in English. As another example, Greek verbs don't need an explicit "I," but there are numerous times in the Gospel of John where Jesus does use an explicit "I" when he says "I am."
3. You will understand commentaries better. Even if they're entirely in English, commentaries will still include discussions of grammar and syntax. By knowing the original languages, you can follow along MUCH better. Furthermore, most commentaries will save particularly technical discussions for footnotes where the original language is referenced.
4. You will understand English (or your own language as applicable) better. Being able to read the original languages and translate to English (or your own language) will force you to know it better. You'd be surprised how many people in Greek or Hebrew class don't know what a participle is. By learning grammar in another language, you must necessarily become at grammar in your own language. That will make you a better writer, and being a better writer will always make you a better preacher.
Look, you can still faithfully exegete the Bible without knowing Greek and Hebrew, but you will be much, MUCH better at it if you do. So I will totally steal the previous answer. What is the benefit? "Much in every way."
Source: Curtis Homan, Facebook chat, 21/4/2021.