What are the Cons of making Primary key or assigning unique GUID value as Partition key in Cosmos DB

Lets say, I have a very huge amount of data inside of a container. I would like to assign unique GUID as value to every partition key property For that container. Now my question is,
What are the Cons of making Primary key or I can say, cons of assigning a unique GUID value to partition key property for every item inside of a container?
By very large amount, I mean the largest possible. or I can say, at what amount, we may start facing side effect, in case of making Partition key value GUID?
One disadvantage I can think of, we will be missing Transactions as it is possible within same logical partition. But in our case, every partition value is unique. What are the others?