Scaling cluster connections independent of cluster size/tier
Currently whenever you want to increase Atlas cluster connections, you have to scale up Cluster Tiers. When an application doesn't require additional disk storage but only additional connections the additional cost is difficult to justify.
The first-order cost contributor to an Atlas cluster is its compute (memory and CPU) requirements rather than storage size. Unfortunately larger and larger numbers of connections require more compute. Note that you may be able to optimize with connection pools.