We are alerting on a card that shows data in a tabular format.  One of the columns in the card is sensitive and shouldn't be sent over unencrypted email.  But the value is contextually important for the person receiving the alert.
I can think of a half-dozen ways around this.  But what I really want is the option to disable the preview in the email when I configure the alert.  Something as simple as adding a checkbox to the compose interface when editing the alert.  It can even be defaulted to checked.