Except for speed or efficiency, any difference in behavior between
arrays with different values of use_fast_arrays is a bug, I think. For
declared arrays and use_fast_arrays : false, we have:
(%i2) array(a,1)$
(%i3) :lisp(get (mget '$a 'array) 'array)
#(##### #####)
OK, Maxima hides the CL array from the user when use_fast_arrays is
false and doesn't hide it when when it's false. How would dropping
support for use_fast_arrays : true remove any functionality to a user?
--Barton