In BF, you can do something like this. In Company Maint / Email tab the SMTP User Name only allows 30 chars. I needed 32 and I think @JohnBroadfoot needed more for his client. Via DFDM I could exceed the dict length of 30. Unless the MAS code specifically does a MID(value,1,30) I will be just fine and so far I have been fine. (Side note: Upgrading to MAS 200 SQL 4.45 and 4.50 will truncate everything after 30)
So ""Skip Source Data Truncation"" is not worded well. It means allow the Customer Name to import more than 30. Assuming it works (I don't know never tried) it should PASS a 31 char customer name with a warning as opposed to a FAIL.