For me, the reply function was the reason for adding it. At the time, Blogger did not allow embedded replies to comments. You had to leave it as a new comment in which case unless the original poster subscribes to that blog post, they will never see your response. And personally, I rarely do that as you end up receiving updates on ALL comments to that post.
I just found out that Blogger now has embedded commenting functionality, allowing replies to comments...threads", if you will. It's apparently still a little glitchy at times but I just switched over as I cannot imagine it being any worse than what Disqus as become.
I'm not sure if the two are related but earlier in the year when Disqus did a huge overhaul, I started experiencing issues with comments not showing up, not being able to reply to them, receiving false notifications, no notification, etc.
So GOOD RIDDANCE! It's gone.
Hopefully back to basics aka Blogger's own, will work out well.