Steve, in my experience it is not that it is "easy" to make "sloppy" connections with compression type connectors; nor is it a matter of "difficulty" very often.
What seems to hapen is that the connection is tightened, then made loose by the pipe, as the pipe gets moved about during installation. Then, after assembly, it's not so easy to get a wrench on all the fittings.
A set-screw, in contrast, is not affected by these rotational forces, and makes the pipe slightly out-of-round, which further resists twisting.
