Should I be shutting down my iMac every night?

What year model and macOS version is it running.

I never shutdown any of my older Mac's running Monterey or earlier. I just let them sleep and only restart them when it is required by an update.

Some of the late model Mac's running the latest couple of macOS versions, are have issues with computer sleep mode. If you have one of those that is having sleep issues, then it is best to shutdown and restart in the morning.

Yes, without a doubt. Is what I do. Starts up in less than a minute, so nothing lost, everything gained.

I rarely shut mine down.

I've used a "Kill A Watt" meter to check the power used when in Sleep mode and it is 0.00 amps.

Likewise, my wife's M1 Mac mini running Monterey and Sonoma still sleeps and wakes as expected without issue.

Sadly others are having computer sleep issues and it hard to nail down exactly what process or service is causing the problem.

for a few examples:

computer restarts with message " Your com… - Apple Community

Mac Desktop not waking from sleep - Apple Community

Mac keeps turning on - Apple Community

I've never noticed any difference with that either.

Mine is a 2021 iMac M1 running Venutra 14.4.1 and haven't had any issues with it.