For script event Updating a field I really miss a phase:
When field is changed

... so that it's possible to run code when the field is changed. In example read from a "link to entry" field and then update another field in the library when the user is working on the entry.

Phase before/after saving the entry is to late as :
- The user should have the possibility to take a look on the value
- Change it if neccessary
- Use "required" if no value is set

... this is only possible if the code is running straight after the field is changed.