It would be nice to have the possibility (in addition to On View and On Edit) to set the form behavior for an On Add event.
It's very common that the user can insert some data when creating the record, but later these data are read only.
Until now I used the workaround with the criteria [Date created]=null, but it make all more complicated by forms with a lot of columns.
There is also an easy way to implement it in the setup GUI. In the "Form Behavior" page there would be a new column "On Add". Per Default this column would have the value "Like Edit".