Numerous months ago I quit deleting old comments because some wanted the history and the ability to look way back.
We have reached the point where there are so many comments on some pages i.e. Sandbox that I need to remove some to get some performance improvements. As it is the page has to load all of the comments–i.e. 1700 on the sandbox that it takes too long to load and this disrupts the ability to post new comments.
I will remove a limited number and see if that improves load times for all of us.