It is not necessary. But if you aren’t happy with the way the speakers sound after performing Trueplay, you can always redo Trueplay and include going up the stairs and see if it improves the audio.

See the ‘tips’ to ensure a good tuning of a room in this Support article... it recommends covering as much of the room as you can:

https://support.sonos.com/s/article/3251

I’d skip the stairs and concentrate on the area of the room where you will be listening to your Sonos.

As said it is easy to try it several different ways and go with what sounds best to you.

In my TV space, pretty much a diamond with open rooms hanging off the front two walls, I concentrated my TruePlay tuning to the back half of the diamond, where all the seating and most of the listening are. Sounds a lot better than when I roamed all three rooms and a bit better than also tuning the front of the diamond space.