When would these two fixes at KMEM be used?
Those are part of the Basic T of the Terminal Arrival Area (TAA).


  The basic design of the RNAV procedure
  underlying the TAA is normally the “T” design (also
  called the “Basic T”). The “T” design incorporates
  two IAFs plus a dual purpose IF/IAF that functions as
  both an intermediate fix and an initial approach fix.
  The T configuration continues from the IF/IAF to the
  final approach fix (FAF) and then to the missed
  approach point (MAP). The two base leg IAFs are
  typically aligned in a straight-line perpendicular to
  the intermediate course connecting at the IF/IAF...
  
  – AIM 5-4-8




They're used in vectoring. Depending on where the aircraft is coming from, it'll be directed to the dual purpose IF/IAF or one of the flanking IAF's. According to the AIM they're not used when traffic levels are high. They can be used with or without a STAR, either way they reduce the workload.


  TAAs are primarily used on RNAV
  approaches but may be used on an ILS approach when
  RNAV is the sole means for navigation to the IF;
  however, they are not normally used in areas of heavy
  concentration of air traffic.


Follows is a brief description of TAA's. (Linked article is also informative.)


  TAA effectively replace feeder routes, and they enable ATC to issue succinct, efficient clearances to RNAV-capable aircraft flying along an airway that passes over or near an airport or proceeding direct toward an airport from any direction. Using TAA eliminates the need for a series of vectors, which also makes them useful in areas where ATC may have poor radar coverage at the altitudes typically needed to guide airplanes onto feeder routes or the final approach course.
  
  – bruceair.wordpress.com