Do you have any idea what your computer actually does?
What is the difference?
Different algorithm but nt so much enaything esle. When exported to either prman or mentalray they get exported as true sunbdivision surfaces (which can be much better in terms of rendered result, especally displaced and especially if you render in prman).
Also the smooth preview is done in the graphics card which is much faster than having maya to pump the data around and then push to the graphics card. This is considerably faster.
I hate getting so many faces on my model because then making changes is impossible
you can allways just go back in time before you applied the smooth, by disabling the smooth node.
Is there a difference or benefit to using the actual Bevel tool?
well yes and no, if you smooth then it becomes a bicubic surface so the edge loop is more likely to be what you wanted if you wanted your corners round, but if you really wanted to bevel then use bevel. In any case please note you also get the same result if you place the 2 bevel edges on top of eachother too.
In anycase theres no right or wrong way, even best is out of the picture there are just many ways to the same result.