Are indexes bloated if using nvarchar field sizes that are much bigger than needed?
Aaron Bertrand's comments copied as an answer:

SQL Server just uses the actual number of bytes for storage, but take a look at your data size estimates - they'll be (half the declared byte size x number of rows) rather than (the average size x number of rows), and this can have a big impact on memory grants. Right-sizing is a good thing. These values can be found in the estimated data size (and any memory grant-related information) in a query plan.