Why you should not increase the number of articles on your homepage
This is a long title for an article, my apologies for that but I was not able to squeeze it into fewer words. Wordpress lets the administrator select the amount of preview articles that appear on the homepage and on every other page. The default value is ten which means that every page (blogurl/page/number) will contain that amount of articles specified.
Google and other Search Engines index those pages and users can find them when searching for keywords. Now, if you increase the amount of articles shown on one page one side effect can hurt your status in Google. Lets say you have 100 articles and a default value of 10 articles per page.
You have decided to raise that amount to 20 articles per page. This means that the last five pages that have been indexed by Google and other Search Engines are not existing anymore. blogurl/page/6 leads to a 404 not found error as do all other pages after that.