I find myself always toggling the Iterate and Iterate table to "Iterate and Append Results". What is an example use case for the default option of just iterating? Can the called project modify the results or what else would it be able to do besides call some other program? I'd recommend the default being "Iterate and Append"
Typical use case for an iteration without appending results is export to multiple files or spreadsheets. We didn't have statistically measured usage of iteration modes, so we defaulted it to the simpler mode so that the transformation requires less setup with default settings, and therefore is friendlier to new users.