RPA does not manage end to end business processes. On the other hand, it is able to mimic human actions on desktop computers, therefore automating tedious, repetitive tasks. Of course, these tasks are performed much faster and without errors too.
BPM – aka workflow – systems are able to manage end to end business processes, and perform all related activities on the server side. Thus, BPM is not able to directly access desktops or mimic human behaviour.
By combining these solutions, the advantages of both systems can be harnessed: BPM manages end to end business processes and invokes a robot in the RPA environment to perform desktop based, previously human tasks. In other words, the RPA becomes a subordinate of the workflow: it starts working automatically on tasks distributed by the workflow, when required by the process, so that the whole process can be performed without human interaction.