The acoustic guitar saddle - while relatively unobtrusive - plays a very significant role in the guitar's sound, since the saddle takes the vibrations from the strings and transfers them to the guitar's top. As such, the saddle is a crucial component of the acoustic guitar's sound, so the shape, construction, and materials used in the saddle are of great importance.
As you would expect, the material used in an acoustic guitar saddle affect the guitar's sound significantly. The material has to encourage a proper balance between tone and sustain. And not just any material will do. Common material in the past have included ivory (now virtually unused for obvious reasons) and bone, though synthetic materials are increasingly more common, including Micarta (used by Taylor, Gibson, and Martin) as well as Graph Tech's Tusq saddles; bone is still a commonly used saddle material. Though metal saddles are common in electric guitars, metal saddles in the acoustic world are considered tone killers. Lower grade plastic is a common material as well, though used primarily on budget guitars.
As opposed to an electric guitar (which has individual saddles), an acoustic guitar has limited options when it comes to adjusting the saddle, simple because acoustic saddles are typically only one piece (though you will find some dual saddle acoustic guitars - I've seen these on Takamines - that offer compensated intonation).
If you wish to adjust the action with an acoustic saddle, it's a relatively easy procedure. You simply sand the saddle down until you've found the optimal height for your playing style. Of course, if the saddle is outfitted with an electric pickup, you won't sand the bottom. Instead, shims are typically used to lower or raise the action.
Regarding intonation adjustment, the options are even more limited. You can replace the regular saddle with a compensated equivalent. Some luthiers perform even more radical "surgery" by relocating the saddle so that the intonation is improved. This involves filling and painting the bridge slot itself, no small task.
Fortunately, there are numerous options for replacing stock acoustic saddles if so needed. There are hand-made options available in composite materials as well as natural materials like bone (I'm a big fan of Graph Tech products personally and find their Tusq saddles to be of very high quality). You can also get saddles that have acoustic pickups built in if you wish to amplify your guitars. I have a custom-made guitar that has an LR Baggs LB-6 pickup that provides excellent tone in both acoustic and electric capacities.
Common issues that arise with acoustic guitar saddles are action (either too high or too low), intonation, and poor tone (often due to cheap materials such as plastic). Depending on the cost of the guitar, it may be worth taking your guitar to a luthier for a saddle adjustment or replacement. If your guitar is worth $200, it's likely not worth spending $100 to get a new saddle set up, though that depends upon how much the guitar means to you.