CCACHE_DISABLE vs. unreadable ccache.conf

Hello!

I'm having case as follow.

$ export|grep CC
declare -x CCACHE_COMPRESS="1"
declare -x CCACHE_DIR="/var/tmp/ccache/"
declare -x CCACHE_DISABLE="1"
declare -x CCACHE_UNIFY="1"

$ ccache -V
ccache version 3.3.3
[...]

When I want to see stats I'm getting:
$ ccache -s
ccache: error: /var/tmp/ccache//ccache.conf: Permission denied

it's ok. Problem appears in such ccache invocation:
$ ccache gcc
ccache: error: /var/tmp/ccache//ccache.conf: Permission denied

man page says:
" The priority of configuration settings is as
       follows (where 1 is highest):

        1. Environment variables.
"

So if I set CCACHE_DISABLE=1 is any reason to read other variables from
config files?

Should be "Permission denied" error in reading conf files critical?
Wouldn't be better to omit such conf file and emit warning only?

Marcin