I don't think it's a question of resources in the form of database space or anything like that, so much as networking and troubleshooting resources.
Troubleshooting forums are incredibly valuable sources of information even for people who aren't members. I know I've solved many computer problems by doing a Google search and finding some forum somewhere I had never heard of where some user had the exact same problem I did, and someone else posted a solution.
The fear, which I think is legitimate, is that when people take troubleshooting questions into private messages, that ends up depriving the Internet community at large of the benefit of that conversation and the wisdom and experience of the folks involved.
I can see how folks might want to take personal, non-tech issues to private messages, and I'm personally okay with that, but it's been my experience that nearly 100% of the private messages I receive on the various forums I use are in fact tech or troubleshooting related, and would probably be better in a publicly-accessible place.
I'm neutral on the subject of leaving or disabling PMs. As I've taken a hands-off approach to moderation and feel that it's most appropriate to let the forum moderators do their job without interference from me, I support their decision.
