Should you use a task killer?

For years now, Google keeps recommending not to use third party task killers, explaining the OS is well optimized for that. Is it the right way to achieve the best run-time?

For years Google has added restrictions to app running in background, to improve battery consumption, is it successful?

I ran tests with and without task killer for the purpose of verifying this in a real use case, no fluf, no bs.

See the results after months running with and without a task killer (click on screenshot for full-screen):

Look at the avg. on-off line, it shows average run-time when screen's on or off. 9 hours vs 7 hours, 7 days vs 2 days. Active task killer is a clear winner here, no doubt, no discussions possible.