In my people's musicianship religion, a choral conductor using a piano to assist vocal tuning is roughly analogous to a Brahmin priest eating a cheeseburger to demonstrate the Vedic importance of food rituals. I.e. not only does it miss the point, it does more harm than good. And it's true that if you always rely on the piano for your pitches, not only do you cripple your ability to grab pitches out of thin air (and hence your foundation for inner hearing), but the tuning itself will be constrained to the piano's not-always-ideal equal temperament.

 

On the other hand, as a recent convert to the religion of karaoke, I believe there is much to be learned by singing along with a recording, trying to capture the nuances of performance. And sometimes---dare I say it?---precise pitch isn't that important, in which case nothing beats the piano for fast and dirty tuning.

 

Finally, if your idea of a good time is La Monte Young's Dream House, you want the best of all possible worlds, and in your hubris you design SuperCollider patches for just-intonation keyboards (TO DO: add link). This is a dark and lonely road that leads to aural hallucinations and friendships with strange bearded men. A simpler solution is to use a recording of a drone, 

 

In the end, it's probably best to avoid any sort of extremism and mix up all these methods.

 

---Ness