Spark vs Brain Module

[Jinto]

I'm wondering what people think the actual purpose is for these two items.
There seems to be a lot of overlap between the two and it always bugs me a bit. For the purpose of this discussion we can probably stick to Beast Wars/Machines and the IDW continuity, since BW introduced the Spark and IDW has made sparks & brain modules a big part of its recent stories.

So according to tfwiki the spark is the 'soul' of a transformer, and the brain module contains the bots thoughts and personality. However we have seen many cases where a spark has been switched between bodies and the 'mind' of the transformer has gone with it.
- Starscream takes over Waspinator in BW
- Megatron in Beast Machines
- Delinquishment Clinics in IDW
- (debatable) *spoiler* The Vehicon Generals in BM were claimed to be the reprogrammed sparks of the missing Maximals.
- (debatable) Megatron going from his Stealth Bomber body to his new body in the recent RID comic.

So what is the point of the brain module? It can't be the transformers thoughts and personality because then there wouldn't be any need for a spark. I mean you could just power it with good old electricity and you'd have a fully operational sparkles transformer, wouldn't you?
And as we've seen in IDW's MTMTE shadow play storyline, a TF can have his mind altered by tampering with his brain module.

But we've also seen bots die when their brain module (computer core in Beast Wars?) is destroyed.
- Blackarachnia is killed when her shell program attaches her 'core' in Beast Wars.
- (debatable) Many bots are indicated to be killed when their heads are crushed or destroyed. This takes for granted that their spark isnt housed in their head.

What do you all think? I'd love some good opinions and discussion about this.