It allows the novice users who are not knowing about the application to go ahead by following the instructions available in the Instructions tab.
This can be achieved as below:
Click on workstep -> Properties and then click on 'Fields' tab. You can enter the description in the 'Instructions' text area field which will be displayed in Instructions field on the workstep form in portal.
You can also link a dataslot to the instructions field. This is useful if you have the instructions to be displayed that comes as dynamic data from users or any other third party system.
The Instructions can be or cannot be same on different worksteps. More importantly the instruction data would be different on different forms which can be easily accomplished by this functionality.