Usually i’m more for plugins instead of workflows, here it is more a personal opinion, but i never say, never develop a workflow to someone, and i develop workflows if they make sense.
In this case, lets assume that for some requirement is better to develop a workflow instead of something else.
Let’s assume as well to make sense that that workflow will be used for multiple scenarios.
So, in here, should we use a long workflow or a workflow with multiple child workflows?
Based on some articles from the SDK and Technet, we should prefer to develop a long one, and why? The reason is that "the overhead occurs when all entities that are used in the workflow are retrieved and the child workflow is started in a two-step process that includes a ‘Workflow Expansion Task’ and the actual workflow instance. Therefore, for maximum throughput, use a single long workflow."
So, "for maximum throughput, use a single long workflow."
Information from CRM 2015 SDK.