McGrath, I'm with you on the session bit. If a participant can't get in tune somehow one of us is going to leave.
I didn't mean to say that electronic tuners are inately bad just that a student will be well served by learning to tune accurately without one. I actually have an electronic one but I never use it. I "inherited" it from my daughter who acquired it when she was young to help her with intonation on her bassoon.
The experience I've had using electronic tuners makes me think the intervals wind up slightly different when set to laboratory precision than they do when set by ear using my method. This may be one of those tempering things or it may just be my imagination. Still, I find that using the electronic tuner takes me longer and requires more minor adjustments afterward.
Keep in mind that I can get totally absorbed in the setup of an instrument. I've been known to spend days "making" a fiddle bridge and setting the sound post exactly where I want it. I've also spent large amounts of time setting up my electric guitar, to the point of redoing the setup for a new brand of strings.
It just seems to me that instruments are so much more fun to play (and hear) when they're properly set up and tuned. Unfortunately, this simple truth seems not to occur to everyone. How many times have you been in a session where someone asked you for pitch, mistuned his instrument, smiled and said "Close enough for folk music."