Implications of using /id for the partition key in CosmosDb

I am from the Cosmos DB engineering team.

You don't have to worry about the number of logical partition keys that are created on a Cosmos DB collection/container. As long as the partition key is an appropriate choice for your writes (subject to a per-logical partition key cap of 10GB) and queries, you should be good.

Implications are:

1. best cardinality

2. easy&fast&cheap document reads

3. no transactions as transaction scope is partition key

4. queries by anything other than id will be cross-partition

PS. I can hardly imagine the case for not needing anything but by id reads/queries. except maybe for document caching (combined with TTL).