Dropping a variable from Pipeline In or Pipeline Out will remove it from the pipeline. If pipeline variables aren't being used by subsequent services, they can be dropped. By removing unneeded variables, you reduce the size of the pipeline at run time, as well as the complexity of the Pipeline In and Pipeline Out displays. This can make the Pipeline view much more usable when you are working with a complicated flow. The term "drop pipeline" implies an explicit cleanup.
Delete is a design-time operation that removes a variable from the current view. It is only useful if you create a variable by mistake. When you change the view in developer after you delete a variable that was previously in the pipeline, the variable will appear again.
