The Save & New button allows you to save a record, and be redirected to a form for creating a new one. This saves two clicks for anyone wanting to create two records, one after another. In the past the button was available, but had to be turned on for each specific table. The new default setting is turned on for every table, but can be turned off for specific tables by inserting the following in PageTS:
<code>options.saveDocNew.tablename = 0</code>
Where tablename is the table for which the button should not appear
More info:
RFC: #9183: saveDocNew for all tables except the option is set to 0
http://bugs.typo3.org/view.php?id=9183