In terms of set-up, do whatever works. There are people setting up open or close for straight shots.
In terms of what's really happening, the ball bounces off the clubface nearly at a right angle regardless of the impact. Spin will be created unless the "initial contact point (ICP)" on the ball stays "in-line" with the clubhead path (CHP), which is an arc rather than a straight line, during impact. To a certain degree, the more the "off-line", the more the spin.
Due to the spherical ball and flat clubface, an opened clubface with positive loft makes contact with the ball at the lower left (or inside) corner, for example.
When ICP is vertically below CHP (positive clubface loft), "back spin" is generated. And vise versa.
When ICP is horizontally to the right of CHP (or closed clubface), "hook spin" is created. And vise versa.
So, for a right-hander's vertically-straight shot (back spin only), the ICP is off to the lower side of the ball slightly to the left (or left of the target line with clubface slightly opened) in-line with CHP (depending on the attacking angle), and stays in-line with CHP while being carried (flattened) on the clubface during impact. Efficient ball deformation and trapping can be enhanced by horizontal hinge action (or forearms roll-over) with more opened clubface at initial contact. It, then, becomes in-line with the target line, which is momentarily overlapped with CHP, at separation.
For a draw (right-to-left or hook spin), for example, 10-degree initially to the right of target line, the ICP is off-line to the lower right of CHP with the clubface closed (yet remained open more than 10 degrees to the target line) to CHP, which is pointing more right than the clubface. It stays off-line with CHP while being carried (flattened) on the clubface during impact, which can be enhanced by horizontal hinge action (or forearms roll-over) with less closed clubface (or more loft) at initial contact, till the clubface is pointing nearly 10-degree to the right of target line at separation.
For a fade (left-to-right or slice spin), for example, 10-degree initially to the left of target line, the ICP is off-line to the left of CHP with the clubface opened (yet remained closed less than 10 degrees left to the target line) to CHP, which is pointing more left to the target line than the clubface. It stays off-line with CHP while being carried (flattened) on the clubface during impact till the clubface is pointing nearly 10-degree to the left of target line at separation. This can be enhanced by vertical hinge action (or forearms reverse roll) with less opened clubface (or less loft) at initial contact.
For higher shot (or a vertical version of fade), create more loft at separation, more back spin or both, which is also enhanced by vertical hinge action, body tilt away from the target, or higher and forward ball position, and so on. And vise versa.
For high fade, high draw, low fade, low draw, hook, slice, ............, well, have fun!!!!!!
