I am aware this is a loaded question. Many of the Android manifests for AOSP, CM, Omni, SlimLP and all of the others seem to start with a blanket manifest for all of the devices they support then, for some, room service will add device specific build parameters and blobs. This makes sense if for those who are building for a range of devices to cut down on server compiling and time to build. As they are building for a range of devices, it does not make sense to spending the time to isolate all of the projects and their dependencies for specific devices.
For the lone devs trying to build a personalized custom rom for the Nexus 5 on their home computer, there is no need to sync projects that are not compatible with hammerhead nor Eclipse development libraries for those who are strictly intend to build. Of the hundred of projects in Lollipop manifest, has anyone stripped it down to the bare essentials needed to build for a device then add projects through local manifests as needed?