Whats the benifit of creating table definition manually in informatica (Source Analyzer) instead of importing

Question

For importing source/target tables, we can either go for importing them from DB/Flat Files/XML Files OR creating the table definition in informatica itself. I have couple of questions here -
•Whats the benifit of creating table definition manuallu in informatica over importing?
•How can we connect that created table definition to the corresponding data source which could be a DB/Flat file/XML etc.
•Please give a scenario where we create table definitions in informatica rather than importing.

Appreciate your interest.

Answer 1

1.There are no "benefits" - I guess it's only an option when you've got the definition, but not the sample. E.g. database object have not been created yet, or are not yet accessible, yet you're starting development already.
2.But the only useful scenario I know is editing - it's far quicker to edit source than import the source if you need to change just length or naming of one column.
3.IMPORTANT NOTE: Source definitions are never connected to any single source instance. This is to represent a structure that will be accessed in future without pointing to any specific table, database, or even server.