The purpose of this technique is if you have a script running on, say, a master host, has a bunch of functions, but has a couple functions that need to run somewhere else (like a backup script that needs to put a remote database server in hot backup mode). You can either write the remote commands to a file, sync it to the remote host (somewhere), then execute it. Or, use this technique to pass the function "live" to the remote environment and run it unmodified.
I personally use it in the front-end client script (snebu-client) for the Snebu backup system.
ssh [email protected] << HERE
echo "HELLO"
cat /etc/hosts
HEREWhereas by using the "declare" syntax, or the attached script in the gist, you can send a number of inter-dependent functions without escaping anything in them (treat them as if they are local), along with the additional complexity you can encapsulate into regular structured programming syntax.
ssh [email protected] <<'HERE'
echo $USER
HERE