In HSMWorks you can preview and simulate toolpaths even while they are being calculated. So if you have a toolpath that is taking some time to calculate, you have the option to continue working by pressing Hide on the Task Manager (if it is visible).
If you select a calculating operation, the preview will show the toolpath generated up to this point. This can be very useful for spotting incorrect parameters - like an incorrect machining boundary - without waiting for the calculation to finish.
Preview for a calculating Scallop toolpath