"Why learn fingerspelling?"

With so many signs available out there, this is one of the most commonly asked questions.
When starting out, in my classes that I teach, I always teach four words in sign language. "How", "do", "you", "sign".
Then they are able to sign "How do you sign" and can fingerspell the word immediately. This saves a lot of time and effort and lessens furstration on the part of the learner. (Of course if you truly wanted to learn ASL, we would learn "Sign and how" to sign out "Sign how" then fingerspell) There are a variety ("How sign", "how you sign", "sign how", and "how do you sign") that depends on the region where you live in.
Secondly, there are a lot of sign language vocabulary, yet there are so many more words out there that has no sign language yet due to the degree of vocabulary. For example- computer hardware, medical words, science (especially chemicals or biology), sports, religion, but to name a few. Fingerspelling can be a life saver here.
Lastly, fingerspelling is used as a tool to establish a new sign before you sign the word. For example: I drove my car into the ditch. I would probably sign this as: "I drove my (lh)C-A-R (rh)3:cl-->ditch"
This means I signed "I drove my" and spelled car then used my right hand to show the "shape" of the car and directed my right hand to show how it got into the ditch.
My point is, with so MANY classifiers out there, we NEED to be able to fingerspell prior to the classifiers. If I did not spell CAR, the audience would have to guess whether it was a car, a motorcycle, a truck, or a van.
Fingerspelling is better than knowing no sign languages- quite a few people will only fingerspell, known as the "Rochester method"