Lemons are great for boosting your immune system, and they also have strong antibacterial and antiviral properties that are good for our bodies. So in a world where the flu and other illnesses run rampant (my state has an outbreak of whooping cough right now), it is important to include this in your daily diet.
Other health benefits of lemons include aiding in weight loss and cleansing the liver. As it aids in digestion, this helps the body use food more readily, instead of store it in fat pockets to use 'later' which is a contributor to weight gain.
A great salad dressing is lemon and olive oil, because of the cleansing properties of lemon and the lubricating benefits of olive oil on the skin, eyes, and joints.
Lemons are also high in:
and so much more :)
These vitamins and nutrients add additional benefits, and it would take a long time to list them all. Here is a good article that helped me answer your Q, enjoy!