I am always focused on reportablity (is that a word) and providing the least amount of code as well as complete 100% referential integrity.  When migrating data from OLTP system...

From my experience, not much if any.

The way that the SSIS engine does these conversion, it has to create a separate stream.

You simply move the complexity from SQL Server (well...

There is nothing wrong with nvarchar/nchar fields.

Unless you look at all the double operations that must occur, and the extra disk space required to store as nvarchar/nchar.

The size of my...

Sarah: Depends on the character. If the characters are non-printable the return blanks. Otherwise they map to non-extended code chars.

I work with overseas (Non-US) data and have to...

Non-ascii (control characters) in SQL field.

Normally, I wouldn't worry about these, however, if you are running a Data Warehouse and use these as dimension attributes, keys, etc. OLAP processing...