Q:

Are you familiar with  tag in html?

I just found that google uses this tag for adsense,
but seems it also works without this tag,why they prefer to use it?

A:

The <ins> tag is used to indicate content that is inserted into a page and indicates changes to a document.  According to the HTML spec this was intended primarily for use in marking up versioning of a document.
Clients that aware of this tag may choose to display content inside this tag differently or not at all depending on what they are designed to do.  This is very much semantic HTML
As for why Google decide to use it I couldn't say

A:

INS is semantic tag describing something that is inserted to the text after the text was already published. It is not a big deal, it is I guess used by their robots to understand something they care about.

