locale: LC_ALL is empty In my ~/.profile

export LC_ALL=en_US.UTF-8  
export LANG=en_US.UTF-8


But $ locale prints empty LC_ALL:

LANG="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_CTYPE="UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_ALL=


How can I set LC_ALL to "en_US.UTF-8" ?
FYI, LC_ALL is an env var you DO NOT want to set from what I have been reading.  It is there for developers for debugging purposes when they need to quickly change all the locale settings ie. env vars you listed above for a particular environment as it overwrites / supersedes all the other locale env vars, thus that is why it is left unset.

cheers 
Chris