According to the user guide for Workflow Solution 8.x you must be a member of the local Administrators group to use Workflow Designer. If you are not an administrator you receive an error when you attempt to create and compile projects. Unfortunately sometimes it´s quite hard to get local administrator privileges from your customer when you are an external consultant/developer.
As far as I´ve found out, Workflow Designer needs local admin privileges because some parts of a workflow project (e. g. shared libraries) are stored below the "Program Files" directory. In an enterprise size company normal users only have restricted rights to access this directory.
Feature request:
Instead Workflow Solution should store the project data in "ProgramData" where non-admin users usually are less limited regarding directory privileges. Thus they would not need to be members of the loacal Administrator group.