Whatever the task, the more complicated he could make it the better, I think it soothed him somehow.
Wow. Same thing at our house. Took me several years to figure this out. But why would the complexity be soothing?
well... here's a go based on my experience and what I've learned from reading about obsessive/compulsive behavior.
The obsessions are what we're anxious over - usually, with OCPD, it's along the general lines that things are not OK.
There's some difference of opinion over whether the anxiety comes first, and we assign specific meaning to it, or the distressing "not OK" thoughts come, and we get anxious over them. Either way...there's anxiety & thoughts about "things are not OK & bad things are about to happen."
So, then the compulsions aim to soothe the anxiety. If I can perfectly control this little corner of the world - the kitchen sink, the laundry, the far left corner of the topmost cupboard, etc. - things might be OK. And the more things I can check off that specific list, the more and more comfort (momentary escape from anxiety) I can perceive I'm getting from doing it. I can do the laundry, and that's soothing because it's a controlled task that gets done within specific parameters. But the brain doesn't stay satisfied with that. If doing the laundry entails 15 steps rather than 10 steps, that's 5 more steps of soothing satisfaction I can get, 5 more things I can check off the list. We add things ultimately to be able to check them off the list. Those lists, either mental or actual, get mentally linked to a perception that we have a chance at controlling how things go and therefore, at preventing whatever bad things are about to happen (but really, they're just about escaping the bad feelings that we often don't even recognize we're having.) So then meaning gets assigned to those lists of activities - that they, not even the end results they bring, but the lists & activities themselves, are the key to controlling the unacceptable chaos around us. If we can just get them right....
The double downside to all this is that the more we reinforce to our brains the escape part, the more our brains get the message that the obsessions are real and need paying attention to. So the more we'll try to escape, adding complexity to prolong the escape. I suppose a rough comparison might be needing more and more of a drug to get the same effect after a while. I don't know how neuroscientifically accurate that is though, or, for that matter, any of this. But it seems to match my experience and to fit with what I've read of OC thinking and behaviors.