If you flick through a whole lot of different radio stations like country or rock, opera, jazz musical theatre or pop you will find an amazing variety of different sounding songs and voices. The art of manipulating your voice and accompanying differently arranged backing instruments is something that that is highly appreciated. When you learn to how to use your voice more fully, you increase your versatility as a singer and make yourself more employable to boot! The ability to sing a variety of different styles can be especially useful when auditioning for musical theatre. Often as a performer you will need to sing a range of styles within a show.
On basis of my experience I can say that you should master one style of singing, but you should have an even hand in others. Especially if you are looking to become a professional, you will find this thing very handy.