I think it should be a full swing so you can let out a little tension. Making a practice swing helps you get loose and sense the motion of the swing needed for the shot. I don't even hit a ball without doing it. It's like if you are an accountant, you turn something on, or if you are a car insurance person, you know numbers. In golf, I have a way of hitting a ball and when I stand behind it, it's like I don't even pay any attention.
Most amateurs seem to have a swing instruction in their mind when they stand over the ball.
Personally, I don't think too much about mechanics. I do that on the driving range. There are a lot of people that do, but there are more that don't. So it's each to his own. You just don't want to get over mechanical.