I’m new to all of this. I’m writing several different pistons… all of them have to do with whether I’m home or not.
Is there any advantage/disadvantage to using a mode (home or away in this example, which is set by a smartapp using the presence sensor), versus using the presence sensor itself?
Regards,
Bill
Your presence sensor could change without you actually leaving your house, especially if you are using your cell phone as a presence sensor. Personally, I don’t use my presence sensor except to detect that I have come home. All of my pistons work off of location mode.
I use Presence Sensors extensively throughout my webCoRE library of pistons without any issue, and find them far more useful than location modes. However, the right answer for you is going to depend on the reliability of the Presence Sensors you are using.
Ryan is correct that some people experience the sensor jumping from present to not present to present again without the sensor (or phone) actually changing location. Whether this happens or not depends on the type of sensor you’re using, your local cell phone coverage, etc. Until you have determined the reliability of your sensor(s) over time, I wouldn’t use them in any mission-critical pistons.
While I’ve never had any significant issues with the ST presence sensor, or with the webCoRE presence sensor for Android (before Oreo killed it, anyway), I prefer using the Tasker/AutoLocation presence sensor for its exceptionally high accuracy, which for me is effectively 100%.
YMMV. 
FYI…I had an HTC phone for long time and I could never use Tasker. My battery life would be decreased to about 20% of what it was before. Could never get a clear answer on why or how to fix it and I just couldn’t deal with having a dead cell phone after 2 hours being away from a charger (I work on the road so my phone is my office). So, I just adapted everything to use Location Mode.
My point is, don’t get too locked into one scenario before making up your mind. Try out a couple different way before setting everything up. Cause once you’re locked into a particular method, changing that becomes a LOT more complicated.