The pedagogy of singing is like a big, steaming cauldron of various ingredients, different sorts of advice and techniques... one has to be careful, as not all of the ingredients you may find are good for you.
I recently was called to step in and prepare a teenager girl from a wealthy family for the grade 7 ABRSM exam.
I certainly wasn't prepared to meet a girl with a perfectly healthy speaking voice but affected by problematic technical faults in her singing voice, voice which could not for the world be ready to tackle any of the repertoire expected for a grade 7 exam.
She produces a breathy sound that she can't carry, for obvious reasons, in the higher part of her voice. Dinamycs are denied, and the tone lack warmth and roundness. Pity, really, considered she tries to sing with emotion.
When confronted with the issues heard and seen in her singing, she admitted that she was taught by her previous teacher, with whom she studied all her life, to pull in the abdomen when singing. She came to like this tone of hers, even though she confessed she was aware of the fact she couldn't use her voice as she was supposed to. Obviously, she was defensive. No one likes when somebody criticize indirectly the teachings of someone you came to like and be dependent on. Alas!
The big point, here is one. And one only.
When one studies singing, during the journey one is bound to be asked to put in place coordinations, or to attempt manoeuvres, or to make sounds that don't adhere with what is physiologically efficient and correct, least with the aesthetics of beautiful singing. If one has a minimum of anatomical, physiological and acoustics data available, one can promptly measure what the teacher advocates against this available-to-all knowledge, thus becoming less of an easy prey for unhealthy
and nonsensical advice which can be highly detrimental and hamper a voice for years - or for a life time, unless someone is never so lucky to meet a good teacher or not humble enough to accept that the problem is at the very base of one singing!
Don't trust everything you are told and don't rely on the use of disjunct information in a teacher studio.
Arm youselves of the shield of factual information, available everywhere and not at all complicated for an average brain, to avoid to be hit in a way that's way too costly for your voice, your self esteem and your future career!