Uses of : (no effect)

nothing

#to officially do nothing
:

#there you go, this could be used when writing or troubleshooting a script and you have only a single item in an if clause

if [ "${this}" == "that" ]; then
  #actually not sure what to do here, let's do nothing
  :
else
  echo "This else, I'll do"
fi

# A novel use I found is to redirect a heredoc into :
# jbeck at Extensis does this in the UTC removal script
#https://support.extensis.com/Support/58278/58411/en-US/Article/View/1004/Uninstalling-Universal-Type-Client-for-Mac-OS/64

: <<COMMENTBLOCK

[ ] 2016-0324: enclose me; love me. i am a block of comments


COMMENTBLOCK

#and replacing the delimiter COMMENTBLOCK allows for a nice header

: << NOTES
Some notes about this script
NOTES