It's basically a good product.
The (hope I'm remembering which nutrients they are correctly) elevations in beta-carotene, vitamin C, vitamin E, folate, and selenium from using Juice-Plus are associated with lower risk---but about that in a moment--of cancers of various epithelial or "lining" tissues all over the body: cervix, uterus, mouth, prostate, etc.
There's also some evidence that you aren't feeding cancer cells by providing your body with these nutrients (the same you might if you, say, took an iron supplement). But I also think the real thing is always preferable, and so do the makers of Juice Plus.
There's always a broader range of nutrients, some science knows about and some science doesn't, in the real fruit or vegetable than in the extract. Also, "ash" is alkalizing. Particularly in cancers that involve the digestive or urinary tracts, shifting the acid-base balance of the fluids involved in digestion or elimination seems to be cancer-protective (and I've seen some really remarkable results in a limited number of cases just from eating fruits and veggies).
But I suppose the main reason I'd prefer not to use the product is, if you're too busy to eat, say, half a grapefruit, you're probably too busy to take care of yourself in other ways. I'd use all that time pressure as a symptom of the area of life that needs to change to give the body a chance to get better.
I haven't taken time to be brief. It is basically a helpful product, and way better than hot dogs and Slurpees. Be well!