What is an actual GOOD reason for going to HR?

I’ve seen so many comments on reddit saying that one should be cautious when going to HR because they protect the companies interests, not yours.

I saw a comment just now where an employee was being repeatedly being made of for being overweight by her manager.

The comment below that said that “this is harassment and you should go to HR.”

Then practically ALL of the comments below that said “no, HR will only protect the companies interest, not yours.”

If this is the case, then what’s the point of even having an HR?