There are different kinds of meditation with different purposes. This shouldn’t be a controversial statement, but sometimes it seems as though there is breath meditation for insight and metta for everything else. Not so. Here are the 3 primary subjects of meditation according to the Itivuttaka:
Monks, meditate on the disgusting nature of your body; practice mindfulness of breathing; constantly notice the impermanence of all experiences. If you meditate on the disgusting nature of your body you will not be not be overcome with lust for beautiful things. If you practice mindfulness of breathing, you will not be overcome with useless thoughts that torment your mind. If you constantly notice the impermanence of all experience, you will be wise.
There are 3 things I’d like to bring out from this little teachings. First, the importance of meditating on the disgusting nature of the body. This is probably the least popular meditation method in the modern world.
Second, notice that breath meditation and meditation on impermanence are listed as two very different and separate things. This is not an accident. The 3 meditation types roughly correspond to the 3 steps of practice: virtue, calm, and insight. Breath meditation and recognition of impermanence are often bodged together as a single practice, but they are not, really.
Finally, each of these types of meditation has a purpose. They are not all the same, and they don’t have the same effect.