Why does this forum (Discourse) want google-analytics?

https://www.google-analytics.com is blocked by my browser, and I do not see any lack of functionality.

What is it for?

It allows google to track how many people use the site, and when they do, outside of relying on when people use google search to get here.

If everyone just types forum.makehackvoid.com in their browser, or uses their bookmarks, then this site could be getting lots of hits that google doesn’t know about, so google doesn’t promote it in their online searches (as they don’t think it’s a popular website).
The same could be said if someone googled a site, clicked on the site, then spent an hour going from page to page on the site. All google knows about is that you clicked one link to the homepage, nothing else.

Adding google analytics to each page means google gets a ping every time someone loads a page, so they can accurately keep track of page views.
Because most websites all want to be promoted highest in google searches, they all add google analytics to their pages.

It will not remove any functionality on your behalf, the only negative to anyone is that google may not promote MHV quite as accurately if everyone of the forums was blocking elements.
Thus, it’s perfectly safe for you to continue blocking it.

(This is somewhat simplified, but it should do)