There are three reasons I know of to shoot with a straight wrist: avoiding torqueing the bow-string, equalizing limb stress, and getting your hand closer to the arrow. The reason it helps avoid torqueing the bow is that you're reducing the area of contact between your bow hand and the bow, which means that if your string fingers exert a twisting force on the string the bow can pivot to eliminate that twisting force. The reason it equalizes limb stress is that recurve bows are generally designed so that the limbs are equally stressed when the point of contact is at the deepest part of the grip; limb stress is important because variations in limb stress will change the point of impact of the arrow. It is beneficial to have your hand close to the arrow because it allows you to change the cant of the bow without significantly changing the point of impact of the arrow.
You can avoid torqueing the bow-string in several other ways than using a straight wrist, primarily by being aware of your string fingers and making sure that the only force they are exerting is a straight-back pull on the string. You will probably find that there is a natural amount of cant that will reduce your tendency to torque the string to a minimum. For me, it is maybe 5-10 degrees of cant.
You can equalize the force on the limbs by letting your hand follow the contours of the grip, but having the main force of the bow be against the web between your thumb and forefinger. And if the force is not quite equalized, the differential in force should not affect the point of impact of your arrows so long as you grip the bow the same each time you shoot.
You can learn to live with the fact that with a low wrist, your arrow will fly differently as you cant your bow, as longbow shooters generally have to learn.
I shoot with a low wrist because my wrist is not strong enough to shoot for many arrows with a straight wrist. This means I'm probably shooting a bow that is heavier than I should be shooting, but that's what I like to do, so there you go. Many better archers than I am shoot with a low wrist. Many better archers than I am shoot with a high wrist.
You shouldn't lock your knees or bow-arm elbow, but the amount of bend is up to you. You can cant or not cant the bow any amount you want, but if you plan to hunt, it will be useful if you learn to shoot with the bow canted at different angles.