[C++] Deciding between "compute function" and "utility function"

[Weston Pace]

How does one decide between "utility function" and "compute function"?
  For example, https://issues.apache.org/jira/browse/ARROW-12739 is
very similar to StructArray::Make which is implemented as a static
function.  However, 12739 would require pool allocation (to
concatenate the list items into one large contiguous array) and array
iteration (to copy into the allocated array).  Does that make it a
compute function?