Thank you so much for the thorough explanation Matt. The issue I have is that I need to create a web app where users will create a feature and then some values will be calculated, for example an id number that will called PlanID that will be created from the combination of fiscal year, county where feature is located and a unique number - if there are no other features in that county, the unique number will be 1, so the id number would be for example 2013-230-001. If there is another feature in that county in that year, the id would be 2013-230-002. So I was thinking I could use a feature service for the user to digitize the features in the web app (I already have a web app in javascript with a editor and I can already create features and populate the date field for example). Then I thought I could use a geoprocessing service to calculate the PlanID, based on the year entered and the county where the feature is located, plus that unique value. I already have a python script for the calculation of the PlanID in ArcMap, but I need to change the script to create the geoprocessing service that will be running in the web app after the feature is digitized. Would this be the best approach - creating a feature service to create features in a web app and then run a geoprocessing service to calculate values based on the features created?
Thank you!