For a stand up bench, you start with your bench vise. The top of the vise should be at elbow height. The reason being that when you use a hand file, it's easier to file a flat surface because of the swing action of your elbow keeps the level. When the vise is higher or lower you have a greater likelihood of filing up hill or down hill.
The same logic should apply to a sit down bench, although an adjustable height chair helps resolve this problem.
Jim my workbench top surface is at 31”. I have an adjustable office chair that lowers, which I lower when doing close up work. I also stand 6’2” so prefer my chair at max height. A portable box one can place on the workbench to bring your work surface closer when needed. Now that I use bifocals I have done that sometimes when doing extreme close up work with the opti-visors. A box about 4-6” high works well for me.
At the moment I am typing this in a standing position. Have the laptop on a box that is 48” next the work bench. It is working really well.
Just for reference, my layout is designed for track at 54”. While many find it high, I think it just right. Remember I stand 6’ 2”, so my eye level is 68”