Bouncer grants a permission to another application temporarily and removes it again when that application is closed. The problem it addresses is that a permission granted once persists indefinitely, and the moment of granting is when the user has the least information about how it will be used.
The mechanism is straightforward and the reasoning behind it is worth stating, because the standard model conflates two different questions. Whether an application may use the camera while the user is looking at it is a reasonable thing to allow, and whether it may use the camera at three in the morning while nobody is holding the phone is a different question entirely, yet both are answered by the same grant. Bouncer separates them by treating the permission as scoped to the session rather than to the installation, so an application that genuinely needs location to perform a task receives it for that task and loses it afterwards, without the user having to remember to revisit the setting. The application declares no internet permission itself, which is the right position for something that necessarily sees which applications requested what and when, since that record is sensitive in its own right.
Newer Android versions have adopted parts of this idea directly, with one time grants and automatic revocation for unused applications, which narrows the gap. It remains more thorough and more immediate than the built in behaviour, at the cost of a prompt each time.
Link: Bouncer on Google Play