More Than One Teacher
Many of the students and/or teachers of old had more than one teacher for their spiritual development. This is because different teachers focus on different elements of the teachings. One teacher, for example, might be an expert on chanting mantras, while the other teacher might be an expert on healing rituals.
Some teachers even sent their students to a different teacher for a while to learn a specific method of meditation in which they themselves were not that skilled. This was not seen as an issue at all, but rather a benefit.
Most of the time a student's main teacher was the one who showed the student their True Self for the first time. But that didn't mean that the student could not study with different teachers.
However, many modern teachers want their students studying only with them as there seems to be a fear of "contaminating" the teachings. The teachings therefore become very strict and if you become a teacher in that specific method, you can only teach that specific way. Plus, if you mix in a different idea or practice, you will no longer be able to teach that system. That way of teaching is in fact very limited. Teachers are there to help expand students' minds, not to narrow them.
I personally see expanding your learning horizons as a wonderful way of exploring different teachers and different styles. Yes, of course it is good to have one main teacher, but it also is good to explore what others are doing and saying. This will help you as a student to gain a much deeper understanding of the system you are practicing. And it will help you to open your mind.
Plus, if we want to be a teacher and want to practice in an organic way which comes from our own heart, then we need to become more fluid. We need to be able to add certain ideas and practices which we personally feel expresses the teachings in true ways that will benefit our students. A spiritual teaching is based on compassion and if we want to teach different students according to their spiritual development, we need to be flexible to do so.
If we claim to be teaching a spiritual practice, then as teachers we need to support students in helping them to rediscover their True Self, which is the ultimate aim in any kind of spiritual tradition. And we can only do that by setting the student free, free to explore and free to expand their mind. If we put our teachings and the student in a box, we therefore are limiting their spiritual growth. If we remove these box-like boundaries and restrictions, then the students' spiritual growth, like the compassion in setting them free, can be limitless.