As its name suggests, half and half is half cream and half milk. It can be used in a lot of things, from coffee to pasta sauces, and many people pick this as an alternative to straightforward creams because its milk content gives it a lower amount of fat.
When used in a creamy pasta sauce recipe as an alternative to heavy cream, half and half can actually be a smart choice as it definitely lowers the fat content in your overall meal. But if you regularly use half and half in your coffee, you might want to stop because you are probably taking in more fat each morning than you really want to.
Half and half isn't made using just any type of milk and cream - it is made from heavy cream and whole milk, which are the two most fatty forms of each of these two ingredients. While using half and half might be less fattening than using cream, it is definitely more fattening than using only milk.
To be sure your morning dose of caffeine is as low-fat as possible, stick to using just milk. Adding a splash of 1% or skim milk will definitely keep your fat intake down.