I liked how, when you had an alarm set up, you could even switch off the phone and it’d still turn itself on automatically in the morning and ring to wake you up. It was actually more reliable than dedicated alarm clocks, since those needed manual time adjustment when there was a winter/summer time change, or when there was a power outage.
Nowadays, I always have to double check the phone has enough charge before going to sleep.
Leaving a lithium battery charging for a long time, even when it’s already 100% can degrade it.
Most devices have failsafes against this, but I still always try to not leave a device charging if its already mostly full… perhaps it’s just me being paranoid, but what I rather do is set up rules so that the phone automatically goes into airplane/battery saving mode at night.