[cuu508]

History can also contain potentially sensitive things like hostnames of non-public systems, usernames, filenames, URLs. I would not want that stuff to hang around indefinitely.

[CraigJPerry]

You can tell your shell to ignore commands started with a space

    HISTCONTROL=ignorespace

Or you can use HISTIGNORE to always ignore specific patterns.

[tandav]

You can also use

    HISTCONTROL=ignoreboth

to use both ignorespace and ignoredups

[berkes]

This is one thing that atuin announced to solve: ignore patterns, keys, passwords. From the announcement I got that it's going to be far more useful than HISTIGNORE. Both out of the box and in abilities.