Re: Turning on savehist-mode by default

[Adam Porter]

FWIW, IME, it may not be a good idea to enable savehist-mode by default. 
 As an example, see this issue report on Ement.el's repository:

https://github.com/alphapapa/ement.el/issues/216

The gist is that, for users who enabled savehist, it was saving the 
variable command-history, which included some complex commands whose 
arguments (from interactive completion) included large data structures 
(which are hidden from the user when called interactively).  This 
resulted in savehist files hundreds of MB in size and very noticeable 
pauses whenever savehist saved its data, from timers and upon Emacs exit.

The worst part was how long it took to discover the source of the 
problem.  There were intermittent reports of weird pauses for months, 
without any discernible reason, until a user finally narrowed it down to 
using savehist.  Then we had to add this hacky workaround in Ement to 
try to automatically avoid the problem.

Such cases may be rare (or not--I can't say), but when it happens, it 
seems to be a bear to deal with, being very unintuitive.  For myself, 
even having written a number of Emacs packages, I wasn't yet aware of 
the command-history variable and how it saves arguments, and certainly 
not the implications of using savehist as well.

--Adam