In a very large partitioned table, updating table statistics requires to sample rows across all partitions and the statistics reflects the data distribution of the table as whole.
If you are maintaining a very large database, you might be well aware of the pain to perform update statistics on a very large table.
A different partition sampling rate cannot be merged together and the syntax constraints made sure this does not occur as well.
There is a database level setting to enable incremental statistics.
Imagine the data distribution remain the same for all previous partitions, and you only need SQL Server to know the changed data distribution for a newly created\loaded partition.
This sounds like a common scenario and now you can manage this scenario efficiently using Incremental Statistics which is built-in on SQL Server 2014 and onwards.