Service stop is killing all nodes not waiting to finish cleanly.

[julianraheema]

When I tried to stop myrobot service "sudo service myrobot stop", all nodes dies instantly rather than waiting to finish cleanly. But when I added this line "ExecStop=/usr/sbin/data-stop" to "/etc/systemd/system/multi-user.target.wants/data.service" the service stop works fine.

My linux is mint 18.
Could you please help me to understand why this is happening?

Update:
When ExecStop= is not exisit, the service sends the signKill by default which is kill instantly, and sigKill cant be captured by ros therefore nodes are dying not in proper way.
https://www.freedesktop.org/software/systemd/man/systemd.service.html
http://man7.org/linux/man-pages/man7/signal.7.html

Extra info are welcome.