proxinator is an iPhone application that communicates with your Mac and locks your computer when you walk away from it and unlocks it automatically when you return. You don't need to type your password anymore - nobody will be able to peek your password through your shoulder. The password itself, stored on your iOS device, is encrypted and it is transmitted in such encrypted version to unlock your Mac when you approach it.
When you walk away from your Mac, the only thing that will happen is that your screen is locked. Your Mac won't go to sleep, nor will it stop its tasks in any way. This means your files will keep downloading, your projects will keep rendering, and your notifications will be waiting for you when you get back to your Mac.