If there is one Achilles Heel of running a purely stock AOSP on Android phones, it would be the need to use an app or widget to quickly toggle Auto Rotate a la Rotation Lock on or off. Android L's inclusion of a Rotation Lock quick setting should help to alleviate this concern for anyone who simply would like to use an Android smartphone as it is, without the need for root or additional app.
To illustrate the point, rotation lock works well in situations where you might want the screen to stay at either portrait or landscape orientation for whatever you are doing at the moment. This could range from watching a movie to reading in which a certain orientation are more preferable. Adding on to this functionality, is that the Rotation Lock quick tile itself would display the orientation it is currently locked on to. This would certainly help in ensuring you are always aware of the orientation and should help in avoiding accidental annoyance and or disruption.
This minute addition is certainly a welcome feature on stock AOSP but for those who are already running rooted or custom ROMs, this isn't much of a big deal. Amusingly enough, this feature can already be found on Kitkat tablets and is finally making its way to phones in general. In this sense, this feels like the feature was forgotten by Google and has now rightfully been corrected. The inclusion of portrait/landscape info however, is pretty nifty in itself as there just might be the tendency to simply forget the orientation you are currently locked in at.