The “Long text and summary” field has a formatter called “Summary or trimmed”. This formatter allows you to trim text to a specified set length which is important if you’re displaying a list of articles. The last thing you want is to have an article display 1000 words on the homepage.
However, this default “Summary or trimmed” formatter cannot trim the summary. If the author enters in lots of text into the summary it’ll display everything.
The Smart Trim module offers a field formatter for trimming text fields. Additional settings are available more than the default “Summary or trimmed” option – an improvement over the default formatter.
Smart Trim can also apply to Text (Plain) and Text (Plain, Long) fields which, by default, do not have the “Trimmed” option available.