There are a number of user privileges that change the user's view (what they see on screen) and this article will show how the view changes and the purpose of the privileges.

View Only Self-Assigned Leads (Search Leads) Restricting the user from only seeing self assigned leads will prevent the user from seeing any leads in search leads that they are not assigned to.

Allow Self Assign 

Allowing users to Self Assign leads will display a button on the lead that will allow the user to assign the lead to them self. This comes in handy when you want users to be able to take leads from another user but not assign the leads to other users.

Enable access to availability calendar of other users Allowing users to access the calendar for other users will provide a drop down list that can be used to change the calendar to another user's/user group's calendar. This can be restricted to only users that are in the same user group so that teams/departments can share calendars without other teams/departments being able to see their calendars.

User can see full details of other user's tasks/events If this option is not enabled alongside enabling access to the calendar of other users, the user would be able to see that another user has a task/event but not be able to see the details of the task. Details being the notes that are added to the task/event.

Enable as Team Manager Enabling a user as a team manager will give enable access to availability of other users and enable them to see full details of other user's tasks/events by default. You then have the option to restrict access to only have access to availability of users in their own group(s) and to only manage users in their own group(s).

Creating a Lead that you don't have the privilege to view 
When a user only has the privileges to see their own or own group assigned leads and there is a lead action that assigns leads to another user/group upon being received, the user will be re-directed to their dashboard with the below error message.

The lead will still be created but the user will not be able to view it.