Whipped cream on a grande drink adds roughly 70–80 calories and about 7 grams of fat; on a venti, closer to 100–110. It is sweetened, so it also adds around 6–8 grams of sugar. On a tall, expect about 50–60 calories.
That makes it one of the highest-impact single extras — more than a pump of syrup, less than a size upgrade. It is also the easiest to skip without changing the drink's identity, which is why 'no whip' is the classic first adjustment on seasonal drinks.
None of this argues against whipped cream on a drink you are having as a treat. It argues for knowing it is there: on a daily drink, skipping it saves on the order of 25,000 calories a year.