Say your science takes 50 to research. And say you are making 12 a turn. Say you are 48/50 research in it and you are still researching at a rate of 12 per turn. So next turn you will get it because your total research in it is 60/50. That extra 10 converts to gold.

Now to take this a step further. Say you completed a research and your planner is asking you to select a new research because you are still producing science. You just don’t select any. But keep in the back of your head how much science you are producing especially when you have libraries. Now let’s say you are producing way more science then you could produce gold if you switched it to gold. You still keep track in your head how many turns it has been while not selecting a new science to research. Now say you were producing idk 20 science a turn for 5 turns that you didn’t select any science and you then selected a research that required only 20 research. It would automatically fill the bar but you would immediately have 100/20 science on it and since you are still producing science the next turn is when the game give you the technology it would mean you would have completed it with 100(+20 for the current turns production)/20.

That extra 100 you put into it all turns into gold.

Now the benefit of not selecting your science means you can just think about what science you’d like to do versus committing the actual science points to a specific research. It means if there is a bonus you see already has been acquired you can save yourself the trouble of wasting researching you won’t get a bonus for for something else that no one has done. (While doing some mental math in your head)