What purpose does the index.xml serve in blogdown?

I'm kinda vague about RSS - which seems to be it's purpose

The reason I'm asking is that after writing my latest post it bloated four-fold to 56Mb. Not sure if it's a coincidence but displaying the site locally after serve_site() also took a lot longer. I'm not sure I want to open it at that size

Is there a way to dispense with it, if not required?

you can open the link in an RSS reader (like feedly) to see it.