When I say Account I mean an organization, company, or department. In other words, conceivably a workflow attribute.
Imagine, for example, a parent workflow that starts an expensive child workflow for each user in the account. If multiple accounts start the parent workflow near the same time, an account with a much larger number of users could monopolize all available workers by simply being first to queue up a large number of activities associated with each user. When there’s no contention, it’s desirable for an account to be able to use 100% of available workers but as soon as there’s contention between accounts it’s desirable to attempt fair scheduling in order to keep latency proportional to account or workflow size.
Obviously it would be possible to partition capacity by creating separate queues for each account, but the result is either potentially significant idle capacity or latency waiting for workers to scale out.