Looking over the rules for reducing insanity and corruption I must say, they strike me as rather odd and lead to some rather odd interactions with the rest of the game.

Making it cost 100 exp to remove a single point of insanity leads to a rather odd case of 'Only the insane will prosper'. A single encounter with something scary could easily cost you more in exp recovering from than you would actually give you.

It promotes a player just going insane and making a new character that is actually on-par with the rest of the group, rather than spending large amounts staying sane.

Corruption is another barrel of fish entirely. Being physically impossible to remove without a very large task makes it almost impossible to manage...and the ways to gain it are silly easy. 1d5 for a conversation with a heretic? Interrogations for information seem likely to result in more cultists very quickly.

The removal is also silly hard for silly little. A meeting with a living saint and the blessing thereof...gives a 1 point reduction? 2 if the GM is generous? That seems so very, very little for so very very much work.

With the loss of the talents that can reduce corruption and insanity gain, it very much is a march to crazy cultist no matter what.

I feel that it could have worked a lot better tied into the acquisition system, with rarities given for various treatments (And the times associated with them). Like a Sister Hospitaler Psychologist or a Pilgrimage Journey.

Well, the game is meant to be thematically about how corruption and insanity are inevitable for any acolyte who isn't very lucky or keeps seeking trouble. The problem is that this theme is represented through an overly granular system with a bunch of extra rules for it. Honestly, you'd be better off pretending that the rules for recovering insanity and corruption don't exist, because they're mostly useless anyway. Or increase the amount recovered to 10. Or make up your own insanity and corruption system.

Inevitable insanity and the destruction of your soul is actually a key part of the setting and mood of Dark Heresy, that has somewhat gotten lost over the many supplements and twists and turns of the WH40kRP line.

As far as I'm concerned, you're not actually supposed to reduce your Insanity or Corruption, but it is there as an option for those characters that makes a concentrated effort to stave off the inevitable corruption and creeping insanity once they feel themselves getting unhinged.

The possibility is always there for certain actions and roleplaying circumstances lowering insanity or corruption, so if you want to, I'd just go for that. Maybe there should've been a sidebar suggesting this as an option, offering the experience expenditure up as a guideline.

After all, 100xp spent represents a characters life experience being spent towards recuperating and dealing with the existential horrors of existence. If that experience is "spent" or if it's simply actions made that represents itself in "pre-spent" experience is really a moot point.

I tend to rule for myself, if Ins/Cor should be "awarded" and in which amount. I like to reward good rpg, so a very heroic or believing character who jumps into some tainted warp goo to rescue a holy artifact or some good people and does so with some pathos, gains a positive modifier to resist.

Also I give the opportunity in game through certain events to get Ins/Cor reduced. E.g. helping an Astrates fight down an seemingly insuperable abomination, should strengthen the believe in the rightness of the power of the God-Emporer and might act as a little relief for the tormented souls...

These are rare events, as I agree the road leads down to a dark and unhappy end...most times.

Newly made characters always gain a certain amount of Cor/Ins, I orientate myself on the group's average amounts and then let them roll some dice. I feel this seems to be right, as a new character on the same XP level, has gained these XP through likewise disturbing and tainting events.