I guess that benefit depends how much you care about legitimacy of ironman/achievements.
The people who say that ironman+no mods is a necessary condition for achievement integrity are correct in theory... and, on observable evidence, wrong in practice.
Go look at the achievement unlock rates for strategy games with a variable scale of achievement difficulty and no such enforcement mechanism, and you will see that easy achievements have high unlock rates, intermediate achievements have intermediate unlock rates, hard achievements have low unlock rates, and very hard achievements have very low unlock rates.
The reasonable, simple hypothesis is that most people either don't care enough about achievements to be motivated to cheat to get them, or care too much about achievements to be willing to cheat to get them.
If people who want hard achievements were routinely willing to cheat to get them, I would expect to see a hard floor on achievement completion rates somewhere in the intermediate-to-hard range.
And, finally: to
actually achieve integrity on Steam achievements requires your game to use Valve Anti-Cheat, which I very much doubt Paradox are interested in doing.
If a game doesn't use VAC, people can use Steam Achievement Manager with impunity, and thus the achievements have, in theory, exactly zero integrity.
(All of this has been discussed at great length in the Vicky 3 forums.)
