Crystal balls, extended sight, mind possession.... there are many ways to go about the seeking of knowledge, and while usually harmless in small doses, the actual use of it can be disastrous. Those who explore divination too deeply often become obsessed with seeing all things. After all, they are usually just sampling knowledge. To know all that goes on in the world is all too tempting. Self-control is encouraged, as well as keeping things to yourself. Knowing more about others than they know about you can be off-putting and sometimes damaging to relationships as one can be accused of breaching privacy. At the very worst, those who use divination too much can find themselves lost in their minds, reaching out to the ends of the world for knowledge... at the same time their body wastes away, forgotten.
Illusionary magic is by no means easy. Creating images, tastes, sounds, smells... it would be easy to lead a victim astray or into a trap. The books of illusion are indeed insightful, but so is their fair warning. Masters of Illusion are rare, not because mastery is more difficult to achieve than other magic branches... it is simply because the promising masters often lose their minds before reaching any state of 'mastery'. Illusionists often lose sense of reality, and can often end up killing themselves, driven mad by their own magic. It is no surprise, however. Illusionists can create an entire living world for victims to live in for however long it be necessary. It is simply a matter of knowing what is real and fake... or sometimes illusionists find their machinations to be more pleasant than reality.
There is no complicated consequence here. Many mages use evocation to summon creatures, spirits, or to draw upon vast wells of energy, or call upon nature itself. Those who have called upon spirits have found themselves possessed, those who summoned creatures were maimed, and those who drew upon mighty storms inevitably were struck down by lightning.
The power to manipulate time and space. The ability to turn something... into another. Surely mages have joked about turning each other into chickens, and leading others through portals that end up in wastelands. Teleportation is by far the most used form of transmutation. It requires skill and precision. Impulsive transmutation can lead to a mage dead inside a wall, or partially in a chair... or another mage. That being said, overextended and repetitious use can result in some horrific mutation, such as warped bodies and a spread of skin boils. Worse is the occasional limb, mouth, eye that is not in its usual place, or worse, an additional one.
Ah yes, the ability to enhance... to imbue an object or person. Some effects are temporary, others permanent. Enchanting has gone to be one of the most profitable magic schools around. Still, it is not without corruptive effects. Enchanters, on many accounts, displayed increasing aggression toward people. They began to feel the act of free will as foolish, and worked to enslave others... keeping everything in control like the objects they enchant.