Damage from your finger can be dirty marks, or wearing away the ink from the handwritten scroll. A yad is merely a means to protect the scroll. Here, Benjamin Berezin is using the Pocket Yad to read from an ancient scroll rescued from "The Last Place of the Jews" in Morocco. The scroll is several hundred years old.
Commonly you see yads made of silver. Silver is beautiful and durable, expensive, impressive, and easy to manufacture. It is a perfect medium for casting the hand figure, and using it repeatedly to make more yads, saving much time.
It wasn't always so. Eastern European yads in antiquity were made from wood, bone, ivory, and metals such as bronze and silver. Sometimes they were embellished with silver or gold, and commonly encrusted with precious or semi precious stones such as turquoise and pearl. Now, yads can be found made of glass, wood, copper, and painted, in addition to the traditional silver.
The carved hand is not required. Many older yads were made with a plain or embellished point. The hand, whether facing left or right, or pointing with a different finger, is up to the maker (and the buyer, of course.) We have become used to the hand and expect it to be there, but there is no requirement for it.
The size of the yad is also up to the designer. Commonly, the yad is stored on the Torah as a decoration. It is considered jewelry for the Torah, embellishing and beautifying the beloved scroll. Along with it are the breastplate and towers. As such, the yads are commonly about 8 to 10 inches long, usually with a silver chain or "necklace" to hang from. Big enough to be seen by the congregation, easy to handle in use.
It has not always been that way. In my research about ancient yads, I found many examples of "pocket yads". Generally presented in a lipstick-case sized box, a person could keep his or her yad in the pocket or tallis bag to carry back and forth to the Synagogue. These pocket yads were probably used for reading along with the Torah portion from your seat and for studying. Very handy.
I also found several examples of very large yads, definitely a sign of wealth and decoration for the Torah.
Yads are expensive. As such, they are not usually personal items but are associated with the Torah itself. Typically a beautiful yad is purchased and donated to the Synagogue to commemorate an event.
Recently, as with most products, modern manufacturing techniques have introduced inexpensive yads to the stores. Now, everyone can have his or her own, and it has become very common to receive one as a bar or bat mitzvah gift.