There are many different opinions about the occurrence of visions during your meditation practice, some people believe that it is a bad thing to have happen, while others believe that it is a sign that your meditation practice is moving into a level of deeper enlightenment.
The main reason why meditators advise that meditation visions are dangerous or cause harm to your meditation practice is that most people will cling to the visions and forget about the goals of their meditation practice, or if the meditation visions are scary they will stop meditating.
The brain is like a tape recorder for the mind, the mind stores everything that you see, hear, and touch, feel, taste and experience on a daily basis from the moment you were born. While meditating these experiences, thoughts and images can come back to the forefront of your mind to be replayed by the brain, which can manifest as a vision or seem to be a supernatural experience.
There are many dangers to focusing your energies on a vision during meditation, apart from neglecting your goals that you have for your meditation sessions, or the negative effects that the meditation visions can have on your meditation practices, becoming reliant on meditation visions or becoming obsessed with the experience of meditation visions will also cause you to fail in your goals of your meditation practice.
The best way to deal with meditation visions is to watch them and let them vanish into the light around you, do not dwell on them or try and create deeper meanings of the visions, treat them with the same disinterest that you treat the thoughts that drift around your head while you are meditating.
There will be meditation visions that will make you feel special, or give you a deeper understanding to your purpose of meditation and your place in the world, these meditation visions are indications that you are progressing on your journey of self-discovery with meditation, but do not focus on the meditation visions, instead continue with your meditation practice with anticipation of the next level of enlightenment.