I was pondering if it was overkill to do the following and wanted to hear thoughts from the community on it.
If I set a data element that is specific to a visitor like a visitor ID or functional role that I always want to follow that visitor I have set in adobe launch the store duration to visitor but in adobe analytics I also have the evar for it to never expire. I did this setup to ensure that the visitor always has those visitor specific values attached to them. Is this overkill? I assume I don't need to store it as visitor via adobe launch but in the event they somehow lose the value I wanted to ensure that it is readily available on the next page load and picked up without disruption.
Short answer is that if you're using the Experience Cloud ID service, the cookie should be all you need. if the visitor ID cookie gets cleared, it's treated as a brand new visitor, which means that any historical eVar persistence doesn't matter. The 'never expire' eVar is tied to the old visitor ID and has nothing to do with the new one.
Additionally, if cookies are cleared, chances are close to guaranteed that cache is cleared too, wiping any visitor data in local storage. In my opinion it's overkill, and that the minimal value gained by copying visitor ID info to local storage doesn't outweigh the complexity and time implementing it. You'll still ultimately get the same trends in reporting.