difference between init and control script? - linux

Question

I am writing a script, for the first time. I followed few examples and I have my init script and then a control script that uses the loop option, to create a copy if itself and start the final application.
My questions are:
1. What is the difference between an init script and a control script? Why is better to implement them separately?
2. Why do I need to create a copy of the control script to start the application (loop), why not do it directly with the control script? What are the benefits of doing it like this?
3. How could I improve my scripts? For example I don't know if using directly kill -9 is the best option, I have read few comments against it..
My init script is very basic:
#!/bin/bash
APPCTL="/home/app/appctl"
APPBIN="/home/app/app.cpp"
if [ ! -x "$APPCTL" -o ! -f "$APPBIN" ]; then
echo "ERROR: app is missing or is not executable" >&2
exit 1
fi
if [ "$1" = "stop" -o "$1" = "restart" ]; then
echo "Stopping app"
"$APPCTL" stop
fi
if [ "$1" = "start" -o "$1" = "restart" ]; then
echo "Starting app"
"$APPCTL" start
fi
My control script is the following:
#!/bin/sh
APP_DIR="/home/app"
APP_CTL="$APP_DIR/appctl"
APP_BIN="$APP_DIR/app.cpp"
APPCLT_PID="/var/run/appctl.pid"
OWN_PID=$$
case "$1" in
start)
if [ -f "$APPCLT_PID" ]; then
PID=$(cat "$APPCLT_PID")
fi
if [ "$PID" != "" ]; then
COMM=$(ps --pid "$PID" ho comm)
if [ "$COMM" == "appctl" ]; then
echo "Already runnning..."
exit 0
fi
fi
"$APP_CTL" loop 2>&1 &
;;
stop)
if [ -f "$APPCLT_PID" ]; then
PID=$(cat $APPCLT_PID)
if [ "$PID" != "" ]; then
kill -9 "$PID"
fi
rm -f "$APPCLT_PID"
fi
for pid in $(pgrep -f $APP_BIN); do
kill $pid
done
;;
loop)
echo $OWN_PID > "$APPCLT_PID"
cd "$APP_DIR"
while true; do
nice -n 10 "$APP_BIN" > /dev/null 2>&1
sleep 5
done
;;
esac
exit 0
Thanks.