From what I've seen watching countless videos:
Most people use hard edged brushes almost exclusively, blending colors by using very low opacity.
But I've seen people use soft edge brushes to lay some blurry colors in backgrounds, or some final blending on very quick paintings (ones that take them 20 to 40 minutes). But for any of the timelapse videos I've seen where the artist claims 2 hours or more, they are using hard edged brushes.
I personally am trying to learn using hard brushes, and not doing very well, I might switch over to soft edges for a while and see where that leads me.
I'm far from an expert though, so hopefully someone else chimes in for ya
Current Artist Level - Straight up begginer