I can found two. Feature ranking is computed to
- reduce the dimensionality, when the number of features is prohibitively large for a predictive model to be applied. In this case, we actually compute feature ranking to perform feature selection.
- be able to focus in later experiments (which may be performed in some biological laboratory and/or may be very expensive/time consuming) only on some candidate features and save some money/time.
Are there any other motives?