Provide the ability to add variables to the subject line of an alert
I created rules to alert when users were added to Domain Admins, Schema admins etc. The company wanted separate subject lines per group. A simple Subject: [USER] added to [GROUP] would have prevented me creating loads of individual rules.
Idan Yona commented
not sure about VSAE, but it actually works in raw xml, there is actually an paid MP that works that way (the OZSoft SAP MP), however a word of cation almost every tool\ extention \additional mp and so on relies on the fact that alertname to alert rule is a one to one relationship, breaking that best practice can cause several issues in the future such as reports mismatches, notification managers misalignment and so on.
if your issue is the subject line in mail notification, i would suggest doing the customization there using custom alert parameters