Workflows support non-linear processes and also a large amount of stages, actions per stage and approvers, workflow engine is capable to cover very complex processes in different industries. Users can customize action buttons and based on the actions the user takes, the workflow will go to a different branch.
For example, if an employee has lost a piece of their uniform, they can fill out a Uniform Request workflow. In the workflow they can choose the reason of request, then each reason will lead them to a different branch of the process, different approvers and results.
Forms are a simple process to accept or reject. The hierarchy of approvals are available but do not support multi-branching process.
For example, if an employee needs to fill out a leave request, and your company has the different flow for each type of leave. You will need to create a Forms template for each type of leave separately.