I pulled a smart list for lead who clicked on an email link (with specific UTM) on a specific date and another list that looks at the leads who visited a page with the same UTM on the same date. Looked at various dates for each. The discrepancy between the numbers range from couple hundred to couple thousand.
Since it is based on the UTM specific to the email, I am not sure why the difference between clicked on email vs visited webpage is so large.
The difference is due to mail scanners that click the link, but do not execute the Munchkin JS (more advanced mail scanners do execute JS, so don't confuse this.with mail scanners in general).