222 rigs
Do remember the 222 for a little while also came in a fractional rig. So there are both fractional rigged and mast head rigged 222's. Most are mast head, BUT the shrouds are still set back like a fractional, so tight upper shrouds will still apply tension to the forestay, like in a fractional rig. With a mast head rig a tight backstay is needed to keep a tight headstay. You could get by without a back stay on the fractional rig, except that it does take some strain off the upper shrouds when running. It could save your mast on a not too controlled gybe. Other wise the best use for the back stay is to add tension to the top of the mast to induce a slight forward bend in the mast(middle of the mast bowing forward) to flatten the main sail when the wind picks up.
Do remember the 222 for a little while also came in a fractional rig. So there are both fractional rigged and mast head rigged 222's. Most are mast head, BUT the shrouds are still set back like a fractional, so tight upper shrouds will still apply tension to the forestay, like in a fractional rig. With a mast head rig a tight backstay is needed to keep a tight headstay. You could get by without a back stay on the fractional rig, except that it does take some strain off the upper shrouds when running. It could save your mast on a not too controlled gybe. Other wise the best use for the back stay is to add tension to the top of the mast to induce a slight forward bend in the mast(middle of the mast bowing forward) to flatten the main sail when the wind picks up.