I find that I don't need to skimp on how many calories in a salad dressing as long as I measure it carefully. That said, sometimes a "light" dressing is just as good as a full-fat dressing for half the calories. As an example, a 2TBSP serving of Newman's Balsamic Light is 45 cals, and the full-fat is 90 cals.
I sometimes use a full-fat dressing but half the amount--for example, a 110-calorie-per-serving olive oil and vinegar dressing, but I only use 1 TBSP. It sounds like nothing, but I've gotten used to lightly dressed salad (as compared to the days when I would just glug in on.

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If I really, really just can't afford that many fat calories, I'll use a salad spritzer instead.
Jay