Find the ergonomic workbench height for your own height.
Bench height is set from your elbow, which stands at about 63% of your stature — roughly 44 inches for someone 70 inches tall. What you do at the bench then shifts it. Precision work wants the surface up near or above elbow height so you can see detail without stooping. General assembly sits about three inches below the elbow, which is the classic 40 to 42 inch workbench. Heavy work — hand planing, chiselling, anything where you push down with body weight — wants it eight inches or more below, because power comes from your shoulders being above the work. Subtract the thickness of any anti-fatigue mat, since it raises you and lowers the bench relative to your elbow. Getting this wrong is the usual cause of back and shoulder ache after a day in the shop.
Workbench Height
Elbow height = your height x 0.63; bench height = elbow height + work type offset - mat thickness
Between 34 and 38 inches for hand-tool woodworking and 38 to 42 for general assembly. The standard exists because it suits a person of average height doing general work — derive your own if you are notably taller or shorter.
Yes, if you hand plane. A lower bench lets you get your shoulders over the work and use body weight instead of arm strength, which is why traditional cabinetmakers' benches sit around wrist height.