WordPress Comments on your blog’s Posts /Pages sometimes can Slow up your blog load time .Which will now be a concern now as Google is considering the Website speed in it’s new Algorithm.
As a alternative to disabling comments you can set pagination for comments which will reduce the impact of comment’s loading on page speed.
If you want to disable all WordPress comments in all future articles by default, go to Settings → Discussion and deselect “Allow people to post comments on new articles”.
Enable or Disable WordPress Comments in Single Click
Doing this will not delete the comments on old posts but it will not allow readers to post new comments on old or new posts.
If you change your mind after some time & want to enable comments them Simply reselect the option again.