Due to government regulations and the desire to have our data as close to our users as possible, there is often a constraint and need to limit data in a specific data center. By placing different shards at different data centers, we can satisfy this requirement.
Every shard is essentially a replica set. We can connect to it like we would connect to a replica set for administrative and maintenance operations. We can query one shard's data directly but the results will only be a subset of the full sharded result set.