It uses proper HTML list markup, which is more standards-compliant and more accessible than separating list items with @Br and S:. Detailed reasons for using this template can be found at WP:UBLIST.
This template can be used with or without {{endplainlist}}. It is an alternative to {{unbulleted list}}, which performs the same function in a more concise but less wiki-style manner. Note that {{unbulleted list}} will work inside image captions, whereas {{plainlist}} does not.