Impact of QAQQINI setting IGNORE_DERIVED_INDEX=*YES

I recently did a little fancy footwork with the QAQQINI file so that I
could temporarily set the IGNORE_DERIVED_INDEX setting to *YES.  This was
necessary to cause IBM's enhanced query engine (SQE) to be used where I had
derived logicals built against a physical file, and I wanted to do some SQE
only functions.  My question is, what if I make this IGNORE_DERIVED_INDEX
*YES permanent.  I was initially afraid of bad query performance, but
through some experiments, it seems rare that the query optimizer ever picks
a "derived index" type logical anyway.

I guess, my more specific question is, under what conditions will the query
optimizer pick a "derived index" since my initial experiments show it not
picking it, despite constructing a logical that should have chosen the
derived index.

The bulk of the offending logicals are DDS built for our BPCS ERP system.
They are often used to control soft-deleted records.