No one can accuse me of not RTFM.  It lures you right into using it to Append Arrays as if it would treat it as a special case.

Insert Into Array Function

Owning Palette:Array Functions

Requires: Base Package

...If you do not wire any index inputs, the function appends the new element or subarray to the end of the n-dim array....

What bugs me about this function is that it does too much work (except when prepending).  The memory management is suboptimal but probably still a bit of a holdover from the days of limited RAM.  Nonetheless, even if LV is a bit stingy when requesting buffer growth, there is still a linearly scaling amount of work being done every iteration.  It is consistent with moving every element every time.

Better than the alternative, but far, far from optimal.