How are SIDs and STARs decided upon during flight planning?

Very true… DP’s/STAR’s are typically (not always) assigned to turboprop and jet aircraft. And in alot of cases turboprops have modified if not separate procedures from jets due to their speed capabilities. In my experiences when flying a turboprop I’d be on a slightly different lateral course until a certain point, then 1000 ft. below overtaking jets. Then when I’m in a jet I’m looking out over the nose for TP coming up ahead and below. A fun perspective and view from either seat…