Juggling balls is very good for you on a number of levels.
Loosening all the joints from your finger tips back to your shoulder blades, improving hand eye co-ordination are the main benefits on a physical level. Use of heavier weights are also good for building muscle in the arms and shoulders. I like three pound soft exercise balls. Five minutes and your arms and shoulders will feel it!
From a mental point of view, focusing on a pattern and trying to make new patterns and tricks is a great exercise for creativity. It is also a great stress relief, as the body and mind are forced to focus on what is going on right there, blocking out thoughts of difficulties dealing with work and social issues. Clearing the mind makes one more efficient and more likely to approach things logically and not emotionally. Reducing stress can reduce hypertension.
And of course juggling is a great way to meet new people and a good topic for interesting conversations and social gatherings.