If you want complete control over the content in your presentation, you can lock it using the Check Out option. Check Out allows you to edit slides without worrying about other users overwriting the content.

 

When you check out a presentation, it reloads in Read Only mode where other active collaborators can only read the slide content. 

Once you are done working on your presentation, you can unlock it and enable your collaborators to edit your slides using the Check In option. Check In allows you and your collaborators to exchange ideas and improve slide content as you finalize your presentation.

 

To check in a presentation,

Click  located at the top right corner of top bar and select Check In. The presentation will be unlocked and your collaborators can start making changes to it.