CX can adapt some templates, but cannot yet adapt most of them. (Update from 2019: This is still relevant for CX2.)
They should be logged in order to know which templates are most frequently used in translated articles. They are not necessarily the same as the most transcluded templates.
This data can be used by the CX product manager and the CX developers to know whether CX can be fixed to support these templates better, and by the on-wiki template maintainers to know which templates should be fixed or imported.