4H is the pencil most frequently in my hand when drawing realism. It is good for soft tones, naturally, but also for making gradual adjustments.
Even in dark areas (dark parts of the hat here for example), first I begin by laying down a coat of 4H. Then I go over it with 2H, making it darker and keeping the tone solid.
Then I will use one of the B’s depending on how dark it needs to be, but only lightly; it will smudge if you make it too dark too fast.
Then I pat it down with a cloth to prevent smudging and go back over it with 2H or 4H. Then repeat with a B pencil, this time making it nearly as dark as needed. Pat down again with a cloth to prevent smudging.
Finally, when the tone is close to correct, I use 4H and 2H to fill in the “gaps” and make the tone solid (if it should be solid) etc.
By “gaps” I mean the little artifacts left behind when drawing with a soft lead. 4H can be used to make the tone of a 6B solid.
Ultimately, 4H was used on every square inch of this drawing, no matter how dark. It is the most useful pencil.