I often heard and read about warmup sets being highly recommended before performing exercises with full working load and therefor do them myself. However now I was wondering, are warmup sets on follow up exercises (Leg Extension after Squats, Flies after Bench Press, etc.) also necessary? Because if you think about it, the muscles were already working on the previous exercise and should already be warm and functioning properly.
Warmup sets are generally recommended for compound movements. As compound movements tend to be more taxing and harder to master the movement, it's beneficial to start with a set using just the bar to work on your form and get your body used to the movement.
Although, if you feel like a warmup set might help you improve your form on an isolation exercise, then feel free to do it.
This kind of question is slightly subjective and what might work for one person may not be ideal for another.