Although auto-climb is not all it does... it is mostly used for that purpose yes. For ease of use, when you launch a new sortie your .speed is automatically set to the best climb speed for that aircraft at sea level (presumably with 100% fuel). It is very usefull for hands-free climbing while you do other things.
Be aware though, that the higher you climb, the farther that climb speed will be from "optimal" climb speed for your aircraft. In other words, don't depend on the auto-speed at the default setting to be your "best possible climb speed" if you are trying to out-climb an opponent at 10k. Better to know your airplane and hand fly it at that point if you are trying to get maximum climb performance.