When deep throating a guy with a curve the right angle can be very usefull in aiding deep throat as the whole penis can be swallowed.
During fucking a curved cock at the right angle can create very very intense stimulation to the male prostate or the female g spot
Yes if you do it well the recipient may well be responding to your fucking with vocalisations of raw unabated pleasure.
Each person is different, for women it can depend on the time of their month, for men it can be their sensitivity or if you can stimulate the second sphincter.
Its finding out where that spot is that creates that effect and yes in most instances you can cause pain with your penis if you wanted to