Keeping similar title in more than one blog post is not good for SEO. Duplicate titles, WordPress allows them by default and that is why many a times it happens that by mistake you give same title to multiple posts and you are not aware of that. The functionality is good because you can keep multiple posts with same title and WordPress will automatically generate unique URLs for duplicate posts which is very useful for hobby bloggers but not for pro-bloggers.
This tutorial is on new WordPress plugin Duplicate Title Checker that checks that title you are using for new post is unique or not. At present the plugin works only with posts but as advertised by its developers, soon you will be able to use it with other custom post types. 
Simply install and activate Duplicate Title Checker and that’s all. Above given screenshots explains everything else. The plugin doesn’t disables default WordPress functionality of keeping same title in multiple posts, instead it provides you an alert that the title you are using is not unique.