Block Heater: Do I risk damage for leaving car block heater plugged in through the 50-degree day?

We're currently experiencing a wide variance between day & nighttime temperatures, with overnight temps falling to +/- 25 degrees, and, daytime temps that creep up to +/- 50 degrees. I arrived home in last night's frigid cold, and, plugged in engine (block) warmer, I didn't go anywhere today, and, below-freezing temps remain the forecast for tonight so -- as I've done under similar circumstances in the past, -- I left the heater plugged in without, ever, giving it a thought. However, this afternoon a passing neighbor noticed the plug, and, advised I disconnect it. He told me that "a couple of mechanics" "warned" him that it's bad practice to leave the block heater plugged "when it's this warm." The thermometer only reached 46 today -- and, only briefly. He didn't know what kind damage might occur, so, now I'm wondering. Is what he said correct? If so, I'll unplug during the day Plugging in is very necessary these nights. Believe me -- I would not go to the trouble of dragging that cord out unnecessarily. Obviously, we don't want to waste energy, but, the energy consumed running a block heater for 24 hours is WAY offset by the amount of fuel/energy burned to warm up a frozen vehicle. Frankly, unplugging was not worth the risk of forgetting to replug -- especially, when the "warm" temperature doesn't last more than an hour. I can't imagine what damage could occur from being plugged in at 46 degrees. Or, even if it were 90! An engine, just running normally, runs way hotter than the heat derived from a block heater ...... right?? Help me out here. Am I missing something?? If so, I'll unplug during the day from now on, and, add "Remember to Replug" in To-Do List in my phone!