Term Frequency is typically not needed for all fields, some CPU (reading one VInt less and one X>>>1...) and IO can be spared by making pure boolen fields possible in Lucene. This topic has already been discussed and accepted as a part of Flexible Indexing... This issue tries to push things a bit faster forward as I have some concrete customer demands.
benefits can be expected for fields that are typical candidates for Filters, enumerations, user rights, IDs or very short "texts", phone numbers, zip codes, names...
Status: just passed standard test (compatibility), commited for early review, I have not tried new feature, missing some asserts and one two unit tests
Complexity: simpler than expected
can be used via omitTf() (who used omitNorms() will know where to find it