One always does, in practice. Choice of pencil is a compromise. Otherwise, there's a constant need to be sharpening a rapidly bluntening pencil. That's why when erasing a mistake, students always an indent left in the paper. FRICTION!You're using a pencil that's too hard for the value you want.
Mostly, the use of compasses in maths and drawing requires light marks, as most are construction marks, and not meant to stand out starkly. (Quite different to an artist's needs.)H pencils are designed to be used for light values.
In my opinion, today's HB pencils are not what they used to be. These days HB pencils seem to be like H or even 2H pencils were a few decades back.