Milk from the usual domesticated animals (cows, sheep, goats) is used not only on its own but also to make cheese, yogurt, butter and cream. These foods are a good source of the easily-absorbed calcium that is essential for bone health. Dairy foods also provide iodine for nerve function, protein for muscle growth and repair and vitamins B12 and B2.
All animal milks (including human breast milk) contain the sugar known as lactose. Almost everyone is born able to digest lactose, but in some people this ability vanishes in childhood. This can cause lactose intolerance symptoms in early adulthood. This affects about 5% of the UK population but is much more prevalent in other parts of the world.
Some people are also allergic to the proteins in dairy products. This tends to show in the opposite way to lactose intolerance, being more prevalent in children and disappearing in adulthood.
Those choosing a vegan diet will also be unable to eat dairy products.
With the exception of coconut milk, plant milks are made by grinding nuts or beans and then adding water. Plant milks often contain some fibre, and with fortification can provide the same micro nutrients as dairy products. All these milks can then be used to make cheese and other similar products.
Dairy produce is an allergy issue for some, a no-no for vegans and does have quite a big environmental footprint. However plant milks do not provide all of the same nutrition and need imported ingredients. As always, weigh up the decision and see what works for you.
the big issue about dairy for me is all the hormones pumped into them. Minimising the amount of those I ingest is something very important to me, especially as a man.
that's interesting about the difference between lactose intolerance and milk protein intolerance - I fear that both might get bandied about rather too much.