Interesting thread. A couple points come up for me:
I have an in-mast furling
main, so the only attachment of the main to the boom is at the end (and the boom is end sheeted). This puts a very obvious compression
load on the boom and it's quite clear to me that my outhaul
line caries more stress than any other line on the boat, and that's pure compression
on the boom. No problem.
Last year I installed a Dutchman boom brake
and love it. It attaches to the boom just aft of the vang, about 1/3 down the boom's length. A thought mostly missing in this thread about a brake is that it's load carrying ability is limited - on purpose - so it allows slippage of the line through the brake when necessary. I can hardly winch
mine down tight enough to get to zero slippage - and you shouldn't anyway. It's a brake, not a preventer. I like how it gently manages my boom in a lumpy sea and the fact that I don't have to worry about any points of over stress in my boom, even in the unlikely event of dipping it into the sea. Also, unlike a preventer, the brake is always rigged and at the ready. Just firm up the line when you head
downwind, or in light airs and a lumpy sea, and the boom is under instant control. I'm fortunate to have auxiliary winches just aft of my cockpit
that I can put this brake control line on, so I have very easy access. It's a great addition to our comfort and lower stress level about accidental gybes.