should compilation-filter-hook be a defcustom?

[Drew Adams]

`compilation-mode-hook' is a defcustom. Should `compilation-filter-hook'
also be a defcustom? I'm thinking that someone might want to save filtering
across Emacs sessions, and this would be one way to do that.

Is there a general policy or guideline that is used to decide which hooks
are defcustoms? There are many hooks that are defcustoms and many others
that are not.