Access Restrictions feature in DJ-Classifieds works as a joomla group filter for submitting ads.
Basically for each category you can choose which joomla group users can SUBMIT ads (it’s NOT meant for viewing restriction - just for submitting).
Once you select the option “Restricted” you can select which joomla group users can ADD classifieds.
Basically it’s convenient when you’re allowing certain users with certain joomla usergroup access to submit ads to certain category in DJ-Classifieds.
If you restrict the category to a certain group other users (from different user groups) wont be able to select this category to submit ads there.