Alteryx's block until done tool is a terrific way to sort which records go to which stream first. However, during the last couple of years my team has experienced several times where there are gaps in functionality. For example, we output data into a relational database (SQL Server) with foreign key constraints. In this manner, one output tool must be completed (the dimension tables) before the others (fact tables) to properly load data. Block until done doesn't always work in these cases, and our team has frequently relied on using chained apps or other clunky workarounds. This creates unnecessary complexity for a simple problem.
A potential solution
Allow an optional setting in the output tool that waits for another tool in the same workflow to complete first.