There are a few mailing lists and issues which should be kept private. This includes certain legal or fiscal issues, and includes (often) nominations and votes on individuals to grant them new access levels. Keeping nominations on private lists ensures that if the nomination fails, you need not be embarrassed. Note that different projects have different norms around nominations, so be sure to check with your specific project first.
Similarly, while all technical and other work on projects is done in the open and is tied to a Committer ID, the ASF does allow Individuals to use a pseudonym when working at Apache. The ASF requires a legally signed ICLA, so we know who is committing code; however they can choose to not display their real name in Apache work.