I am trying to work out if based on a trigger to change a mode or routine? My take is a routine may trigger other things, so might ultimately change that if it then triggers it’s a mode change. What are peoples view on this.
You can have a Routine change a Mode, so you would essentially be changing both (if you wanted).
You can have a trigger directly change a mode (such as your presence being gone sets the house in Away mode) and that totally makes sense. But you could also have it fire off a routine (your presence being gone turns off all lights AND sets the house in Away mode)
It all comes down to personal preference. There are multiple ways to get most things done in ST. You can use the standard Routines or you can use a custom SmartApp like Rule Machine. You can use Smart Home Monitor or Smart Alarm.