In WordPress it's very common to use the wpautop() function. It's a very handy function for converting plain text into paragraphed & semi-formatted content. However, if you're using this function alone you could be missing out on a lot of functionality that you could easily get simply by applying the_content filter instead. To show why the_content filter is so much better, let's take a quick look at what both of these do.
This function is very straightforward - it wraps your line-broken string text in <p> tags. From the repository:
Changes double line-breaks in the text into HTML paragraphs (<p>...</p>).
Pretty basic, right? It helps you to display your string content in very organized fashion.
apply_filter( 'the_content' )
This filter runs the content that you feed it through several functions:
wptexturize - Converts special characters such as ... into the proper html display
convert_smilies - Converts text such as :) into...