The biggest thing most modern catamaran masts do is allow you to flatten the sail to control the amount of power you have as the breeze increases. Most sails are built with some luff curve, and most mast a built straight. So you add diamond wires and add some prebend into the mast, but its still straighter than the sail (if the sailmaker has done his job) This causes the sail to be full and the sail in this shape produces lots of lift (power)

So, without any downhaul, you have a very full sail shape, which is good up until the boat begins to heel to much in puffs. Adding more downhaul bends the mast back and gets the mast closer to the prebuilt luff curve of the sail, and flattens the sail. This allows you to go faster in higher winds. So if you are sailing in higher winds and the boat feels sticky or overpowered in gusts, add more downhaul. Modern wing masts like the Acat masts are really good at this. You can actually play the downhaul instead of the main on the HT, which has a modern wing mast. This is really fast by the way.

A really good example is an airplane wing. When you are taking off, and landing you need full power with lower wind, so the pilot has uses lots of flaps (think full sail shape) When the plane is crusing along the flaps are retracted and the wing is less full, (think flat sail shape)

Fore and aft bends helps with flattening the sail and works with downhaul. You also want some sideways bend, which needs to bend differiently than the fore and aft. Most masts (modern wing masts) are more stiff fore and aft than sideways. This sideways bend helps with the mast twisting off in a gust. Diamond wires keep the mast in column depending on your weight, so the top can bend off, but the middle stays straighter side to side.

The Acat masts a built with two bend numbers in mind. The first is the sail makers luff curve and sail charactoristics and the second is the weight of the sailor - which influences the side bend of the mast.

The net is that a mast needs to bend, but in a very specific, very calculated way and bend differiently fore and aft vs side to side. Rotating wing mast on catamarans are actually some of the most advanced masts and sail combinations on the water, not counting a CClass type rigid wing sail. Cat rigs are way more efficient than monohull masts/sails and its one of the reasons modern cats are so fast.