I also don't need a calculator but I regularly use one to do even simple arithmetic operations, because it speeds up the operation and guarantees a certain resu

I also don't need a calculator but I regularly use one to do even simple arithmetic operations, because it speeds up the operation and guarantees a certain result with given inputs. The purpose of an SDK such as jQuery is to help a developer do common tasks without needing to write his own library. If it's used widely in the industry then even better. If it's open source, even more betterer.