Hi Will,
I think the main 'pro' for having a few more sections is so new users know where to post questions / start discussions, where they will be seen and not bogged down with other threads.
With only having 4 sections, it's not easy to work out where your post should go, and if you can't find a relevant section then you're likely to find another forum somewhere else to post in.
Lets say you have a question about using ladders on site, or 110v tools. It could go in either general or H&S, but if you need an answer quickly you want them to be in a section thats going to be read by someone who 'knows' what they're talking about. You'll probably find alot of users will only bother looking in sections they know about.
Maybe expand the Plant & Machinery section to cover Tools & Equipment, H&S split into sections for people who implement it, and the worker who has to work by it etc.
And definately a Suggestions section. Good way to get feedback and ideas!
Thats a few of my ideas anyway!
Dan
Another thing to get a few more regulars would be a jobs section. With the trade as it is at the moment, there's plenty of people looking for work and could be a good opportunity to get some knowledgeable tradesmen on board to help out with questions.