TFRGRPJOB vs ACTGRP

Hi,

Been looking at the possibilities of running a program using a different
library list than the caller. Particularly as the program is a large OPM
calling lots of others all copybooked in, I've been looking at TFRGRPJOB. I
have to submit my analysis, and I'm pretty sure I'll be told to convert
everything to ILE and use an ACTGRP to keep things isolated from the
calling program. I'm hard put to think of an advantage of running the
program in an activation group rather than a group job. Here's one: when
using STRDBG you can step into the called program.
Any more?
Thanks!