What is the comments limit for and how can I change mine?

As it states, this limits the amount of comments displayed when viewing a deviant's artwork or while browsing news articles, journals and more. If you set this to 25 and the artwork, news article or journal has 26 or more comments, then links will appear under the first 25 comments "Previous Page 1 2 3... Next Page" allowing you to page forward or back through the other comments.

You can change the number of comments you see per page by visiting the 'Browsing' tab in your settings page. On this page you will need to navigate to the 'Comments' section, located on the right of the page, next proceed to the option entitled 'Comment View'. You will then be able to change the number of comments you view by selecting the 3rd drop down menu, next you may choose a number. Once done click on 'OK' and your new options will be saved.