Is meditation useful?
Meditation with the intention of experiencing higher or peaceful states may be successful. And then those states pass and the other side of the pendulum comes into play. Then one meditates again, and goes into the states again, and so on.
Meditation with the intention of inquiring into who experiences states, that is, the Subject of experience, may lead to Enlightenment, which means uninterrupted peace beyond the pendulum, with no compulsion for experiencing, or search for, this or that state.
There is evidence that meditation can be useful for other purposes too. It depends on what one wants and on one’s degree of understanding. It can be important in analyzing the observations about the psyche and in eliminating what is useless and harmful.