Voices are a lot like wine. One might be perfectly suited to one set of circumstances (venue, mood, style of music, emotion, etc, etc) on any given night, but the very same voice might be completely unsuited to the circumstances of another setting. And, like wine, too much of a voice can leave you feeling ill.

There is also the reality that vocal intervals within any octave are not the same as the "concert pitch" instrumentalists are accustomed to. An experienced vocalist will usually adjust to the instruments, since the instruments can not adjust to the voice. Instrumentalists will sometimes criticize an unaccompanied singer when they hear the difference in vocal intervals in contrast to what their "concert pitch ear" tells them they should hear. There is a current thread on "perfect pitch" that nicely complements this one.