Recent article by Don Street states :
"Most cruising-boat masts are sufficiently overbuilt that when the boat is hard on the wind, the leech of the main will support the load of the staysail stay"
I don't think so !
When going hard on the wind the load on the leach of the main and the staysail sheet are both in the leeward side of the boat. The load from the staysail is transferred to the forestay and then to the mast...on the leeward side of the boat.
When going to windward, through and over waves the loads are magnified. There needs to be a counter force on the windward side of the boat to prevent the mast from pumping and perhaps coming down.
Running backstays need to be rigged from the attachment point of the inner forestay (preferably at or close to a spreader, on the mast, run towards the stern through blocks attached to solid attachment points.
When going to windward, the windward runner needs to be winched on tight to provide the counter balance to prevent the mast from pumping.
I think the advice given in the article referred to is dangerous.