Consider this scenario:
You have a layer in QGIS with nice labels that you took a long time designing (customizing its multiple label options). For this you used "show labels for this layer" in the labels top drop-down menu.
Then you decide you want slightly different labels for different features within the layer. Now you need to change "show labels for this layer" to "rule based labeling". However when this is done, all the hard work customizing the first label is lost - you need to start from scratch over again.
Does anyone know a way to copy the style and options you defined in "show labels for this layer" and convert it into one of the list entries within "rule based labeling"?