There is a feature called "skipExpression" in the eclipse plugin that allow developers to provide an expression using which the activity will be skipped at runtime if evaluated to true. However this feature is not exposed in the APS editor and hence customers/prospects are not able to leverage this feature when using APS!
You can find a lot of discussions in the community around this feature. Eg: https://community.alfresco.com/thread/226024-skip-expression-on-user-task
As descibed above
Make this property available and configurable on all the applicable activities (service task, user task etc) in the APS process designers.
This is a very useful feature that can help implement case management scenario where a decision to execute/skip a particular step in the process can be calculated dynamically!