The project layer filter allows you to quickly select a layer
from the current project and highlight it in the layer tree.
It's useful for complex project with lots of groups, where
it's easy to "lose" layers somewhere in the tree...
The composition filter allows searching for and opening
compositions from the current project
These may represent additional layers such as layers which
are not included in the map layer registry, or paths to
layers which have not yet been loaded into QGIS.
