"I know this word" vs."Ignore this word"

what is the difference between these buttons:
“I know this word” and “Ignore this word”
because when I use “Ignore this word” it acts like “I know this word”

You can see a counter “Known Words” up in the menu bar. “I know this word” adds to this counter (you have to refresh page or to move to another page to see it updated). “Ignore this word” does not. The difference only in statistics.

You would want to ignore words written in languages different from the one you study, names, geographical names, etc.; so the “Known Word” counter closely corresponds to the number of your real vocabulary in the given language.

Then you can divide the number to some factor (depending from the language) in order to get rough estimation of your vocabulary in terms of dictionary entries (i.e. write/wrote/written is a single dictionary entry, but 3 “known words”). For English it will be 4, I think. So if your “known words” counter shows 10000, then it will be around 10000/4=2500 of dictionary entries. They say you need the vocabulary starting from 8000 words to pass TOEFL test.

Ignore this word - This word will be removed from all of your statistics. It will not show up as a Known word. You can use this for words that are not in your target language or names if you don’t want these words added to your statistics. You can also ignore words you don’t think are important or that you don’t want to learn later. You can always highlight these words later on if you decide you do want to learn them.
Make known - You are telling the system that you know this word and it will be added to your Known Words total which displays across the top of the page.

Thank you for explanation!

It is very useful for me to use this function “Ignore this word” for automatically split characters when learning Chinese on LingQ.
Many words are mistakenly picked up when contents providers do not put space between meaningful words.
And it is also useful for us to use this for miss-typed words called typos.