Why do we say "right-hand side"?

I suppose that hand is used to distinguish from right as in correct.

Handedness is perhaps the most common way of teaching someone left from right. While there are other natural things that exhibit consistant directionality (the circular flow of water in a drain in a given hemisphere; the rotation of the earth when seen from above a particular pole, etc.) none is as readily accessible to the viewer as her or his own handedness. Most of us know from an early age which of our hands is dominant, and that is labeled by our elders as either right or left, depending on our proclivities (let's skip the brain dominance discussion for now).

We can then identify whether the direction or side we are considering corresponds to our right or left side, based on our knowledge of our dominant hand.

I think the hand reference when discussing side is a reflection (residual) of this basic analysis we learned in our youth.

My husband and I have been 'discussing' this for years. If you look at a 'thing', e.g. car or boat, the right or starboard side of the boat is on the left hand side as you face the boat, but it is still the right side of the boat. I say the right side of the boat is always the right side. Key word is 'OF' - the side belongs to the boat. Same with a piece of furniture, etc., but as you face a piece of furniture, the left hand side is relative to the person facing the furniture. Same with N, S, E, and W on a map. E is on the left side OF the map but it is on the left hand side as one faces it.

I always thought right/left hand side was used instead of right/left side so you could be clear about a location.

For example, when something is on the right hand side of the dresser, if you are facing the dresser, it will be to your right, not on the actual right side of the dresser from its point of view, facing you.