To improve the usability of large QGIS projects, we now support direct drag and drop of layers from the project table of contents to any widget which asks for a map layer selection (e.g. Processing algorithms). For complex projects, locating a layer in the table of contents and dragging it is much easier then picking it from the flat map layer widget combo box!
Additionally, for Processing algorithms, layers can be dragged direct from the Browser panel to input layer choices.
This feature was developed by Nyall Dawson (North Road)