Lights and computers bouncing off are inconveniences, it really shouldn't happen. Panniers coming off can be a safety issue. There really is no excuse for using a pannier that can bounce off. Locking mount systems have been widely available for about 20 years. I used a hook and elastic system on cheapo panniers about 20 years ago but these days every bike shop stocking panniers have proper, safe versions.
People advising the use of hook and elastic should be locked up.
Even some locking mounts are dangerous. If/when the lock mechanism breaks, the hook comes off. Proper system fail in a safe mode, ie with no lock but a working hook.
\end_rant