I used to be rather dismissive about this; but (as with several of Wilber's concepts) more recently have come to acknowledge this as an important concept, especially in relation to the abusive guru phenomenon (Wilber comments on this too, in relation to his old guru Adi Da).
Sure it didn't seem to fit in with Wilber's over neat compartmentalizatuon (and still doesn't), but seems a useful way of understanding uneven spiritual development.
from Wikipedia - Ken Wilber page:
Lines, streams, or intelligences
According to Wilber, all holons have multiple lines of development, or intelligences—in fact, over two dozen have been observed. They include cognitive, ethical, aesthetic, spiritual, kinesthetic, affective, musical, spatial, logical-mathematical, karmic, etc. One can be highly developed cognitively (cerebrally smart) without being highly morally developed (as in the case of Nazi doctors). However, Wilber acknowledges, you cannot be highly morally developed without the pre-requisite cognitive development. So not all of the developmental lines are ontologically equivalent.
Lines of Development and the Integral Psychograph - Ken Wilber - Integral Life