Although singing is a natural process, it can be improved in quality, range and accuracy of pitch and rhythm just as an instrumentalist can improve their ability with practice.
Since it is the brain which issues the information for singing, it is most important to train the brain to recognize sounds and to build up a bank of knowledge which makes it easier to understand the whole process of making music.
This has the added benefit of helping you to relate to what other musicians are playing and understanding the way a song’s melody and its accompaniment work together, as well as making it easier to understand the sheet music of any song you wish to learn.