Is raw celery good for you? Not really, or more accurately, not for one of the purposes it is most frequently used.
Next time you buy a fresh cold-pressed juice, take a look at the ingredient and nutrition label. It doesn't matter if it's a national name brand like Evolution Fresh (which is owned by Starbucks) or lesser known regional producer. For almost all of the vegetable blends, the first ingredient you will see listed is either apple, celery, cucumber, or a combination of those.
Now there's nothing wrong with those 3 ingredients. In fact, they can be very nutritious and healthy for you, especially red delicious apples (with skin) which have an ORAC of 4,275, almost the same as conventional blueberries. When it comes to celery and cucumber, they are an excellent snack and salad accessory. It isn't really true that celery is a negative calorie food - in other words - your body does not consume more calories to break it down than it contains. The thermic effect of celery is around 8%, which means 8% of the energy is needed by your body to digest it. A food would need a thermic effect above 100% to really be a negative calorie food. That said, celery is such a low calorie food - 1 cup chopped (about 3.5 ounces worth) is only 16 calories.
This makes celery a perfect snack for dieting so long as you aren't dipping it in a high-calorie sauce or dressing like ranch (try low sodium mustard or oil-free hummus instead). But what raw celery is not perfect for is juicing. Why? Because it contains a very low amount of antioxidants, vitamins, and minerals for a vegetable. However given that it's so cheap and has high water content, juice manufacturers love to use it as a base or primary ingredient in their products. Why is celery bad for you when used this way? It's not that it's unhealthy per se, but rather your juice is a lot less nutritious than it otherwise could be, if a vegetable/fruit with higher antioxidants was used as the base (and most would provide higher content).
USDA Database for the Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 - Prepared by Nutrient Data Laboratory, Beltsville Human Nutrition Research Center (BHNRC), Agricultural Research Service (ARS), U.S. Department of Agriculture (USDA) - May 2010