The difference is that it means the torture is necessary, and short of inventing a new method the MC will have to continue Harrowing to fuel large scale Theurgy. Previously, with the understanding that it was just blood, Harrowing could simply be dismantled as there are plenty of ways to nonlethally harvest quantities of blood, not so for brains. Now the MC has to seriously consider what the Harrowing alternative is, if there will be one at all.
True! This is a good moment for that to come up again, if the MC can mention that they have already seen the internal mechanisms of a Harrower.