I have no idea if it's still an issue, but ~1.5 years ago, I was sorting through my email, and discovered that a small plain text message was taking up >3MB in my inbox.

I dug in a bit, and it turns out that Grammarly was embedding a gigantic amount of code into the email messages in the form of stylesheets and other things.

Needless to say, after raising it up the chain, we had the extension blocked company-wide.