Louis Davidson runs some tests:
If you have ever done any performance tuning of queries in SQL Server, no doubt one of the first thing you have heard is that your search argument data types need to match the columns that you are querying. Not one thing in this blog is going to dispute that. Again, the BEST case is that if your column is an
nvarchar, your search string matches that column datatype. But why is this? I will do my best to make this pretty clear, especially why it doesn’t always matter.
Read on as Louis lays out the explanation.