This Views plugin makes unformatted styles, field row styles and other output more readily configurable without needing to override template files. Instead of overriding row style templates for views where you want to specify different HTML elements (tags) and class attributes, you can specify these inside the Views UI and avoid overriding templates for each view.
Some of Semantics Views functionality can be done in Views, but Views is restricted to use only predefined HTML element and can only style each Field but not wrap rows with any HTML you like.
For more info and usage, check out the documentation on Drupal.org.
Scott from LevelUpTuts has a short tutorial for Semantic Views for Drupal 7, you can find it on youtube.