The purpose of this extension is repetition of foreign words.
Just for example, I am a native Russian. When I read English article in Chrome and unknown word is coming up, I am double clicking it, and Google Translate Extension (I have it installed) provides popup with translation, grammar and pronounciation.
So far, so good. So what is the problem? The problem is, that such unknown word is relatively rarely appears in texts that I used to read. So, the next time when I will meet it again, can occure after weeks or even months. And untill then, I will forget this word. For sure. (Read about forgetting curve.)
The solution for forgetting new words is so called spaced repetition. And this is what this extension for. It takes information from Google Translate popup and stores it to Chrome's local storage on my laptop. And then it repeatedly shows it to me after increasing intervals of time.
With default settings, each stored word will be shown 7 times. After 1 hour, then after 2 hours, then after 3 hours and so on.