DFTACTGRP(*YES) vs ACTGRP(*Caller)

I have seen the below on some post...........

Programs compiled with DFTACTGRP(*YES) do not behave the same as
ACTGRP(*CALLER), even if the ACTGRP(*CALLER) program was called from the
default activation group. This is because specifying DFTACTGRP(*YES) does
more than control which activation group the program is compiled into,
it also controls some other OPM compatibility things.

I have seen post that say DFTACTGRP(*YES) was to help RPG programs convert
to ILE with out all the goodies of ILE, but still use SEP, content assist
etc.. CRTBNDCBL for cobol does not have a DFTACTGRP parm just ACTGRP parm.
So can I assume using ACTGRP(*CALLER) in cobol is similar to the DFTACTGRP
(*YES) that RPG has? Not sure what the other compatibility things are?

If I have Cobol "Program A" calls "Program B" and "Program B" is a program
that gets used all throughout the system not just in my "Program A" Call
"Program B" application. If I am changing just my application to ILE would
making "Progam B" ACTGRP(*Caller) be the way to go since other applications
that are still ALL IN OPM COBOL will still be calling "Program B"? Has
anyone done something similar and sees issues with this thinking, because
one post will say one thing and the next another? Or did you create
duplicate programs one for ILE and one for OPM?

Thanks,
Jeff Buening