Decks, Patios, Porches and Docks - Do I need to sand?

We are refininshing our deck which is about 16 years old and in good condition structurely. We have completed all the railing which we pressure washed, sanded, primed and stained with a solid color latex stain. Looks great, but lots of time consuming hard work. For the floor, we decided to use an oil based primer and stain (probably Cabot). After power washing the deck looks much better than expected. We plan to replace some of the splintered boards and rent a floor sander to prepare the wood for stain. Some of the wood looks so good, I'm wondering if it is necessary to sand the entire surface or just use the small belt sander to smooth the boards that aren't smooth. Does the tape test work good to make this determination? More than half the deck is covered, so I suspect that is why it is in good condition.

I don't know what the tape test is.

If you are using a solid stain you shouldn't need to sand any more than is neccesary to give all the wood the same/similiar "texture" You also probably don't need a primer under the stain but a lot depends on the color of the stain and the type of wood.

Thanks for the help. The tape test is where you put a piece of tape on the wood and pull it up. If you have wood fibers you need to sand and if not you don't. Some of our boards obvisously do need to be sanded. Others I think I will try with the tape just to be sure. We've spent so much time on this. I want to be sure it is done correct to prevent problems.