A two-byte Partition number is added to the ROW-ID and it is now called a ROW KEY. The two-bytes per row will add more Perm Space to a table.

Joins to Non-Partitioned Tables can take longer and become more complicated for Teradata to perform.

Basic select queries utilizing the Primary Index can take longer if the Partition number is not also mentioned in the WHERE clause of the query.

You can't have a Unique Primary Index (UPI) if the Partition Number is not at least part of the Primary Index. You must therefore create a Unique Secondary Index to maintain uniqueness.