When editing the Load File step of a workflow, if you turn on the "Detect structure from a new file" option, then upload a new file, all of the columns on the Column Definition are reset to the Text data type and lengths of 255 characters.
This is inconvenient when the new file structure is similar to the old file structure, perhaps different only in the additional of a couple of columns. All of the previous changes to data types, lengths, value mappings, etc. have to be recreated.
If Campaign detects that a column in the newly uploaded file has the same name and data type as an existing column definition, then it should not change the data type, length, value mapping, etc. This will reduce the rework needed when deriving the structure from a new file.