Virtually every health authority recommends that we get 6-8 servings of vegetables and fruits per day and very few of us actually get that. Juicing is an easy way to virtually guarantee that you will reach your daily target for vegetables.
While you can certainly juice fruits, if you are overweight, have high blood pressure, diabetes, or high cholesterol, it is best to limit using fruits until you normalize these conditions.
The exception would be lemons and limes which have virtually none of the offending sugar, fructose, that causes most of the metabolic complications. Additionally lemons or limes are amazing at eliminating the bitter taste of the dark, deep green leafy vegetables that provide most of the benefits of juicing.