As Google and other search engines penalize sites that have duplicated content, you may want to use post excerpts everywhere other than the single post page. But in order to do that, you would have to edit your theme files which might be a big trouble for those who are not familiar with php codes. This is where Post Teaser plugin comes in handy.
This plugin actually generates a preview or “teaser” of a post for the main, archive and category pages, with a link underneath to go to the full post page. It includes features to generate a word count, image count, and an estimated reading time as well.
You can edit how many words that will show in a post. For example, you can set the plugin to limit every posts to 100 words and set whether to show the word count, image count and the reading time. Basically this is the simplest way to make post excerpts in other pages other than the single post page without changing the codes of your theme. 😛