My experience is some brush will almost always hold fish. I usually catch some there, so I don't scan it, I just fish it.
Other areas have many trees or brush and I scan until I see fish on or near.
I might scan once and throw out 3 markers on the areas as I go over them (downscaning).
However, it is a sad fact that seeing fish doesn't always mean catching fish.
I caught 2 last time out. I SAW 100 + on the sonar.
I left early.