For most of Yr 10 and 11, when I was 14/15/16 in the mid 90's, I was left home with just my DSis, who was 2 years younger. It was 'unavoidable' as our DM was in a secure Psychiatric Unit and our DF worked away during the week. He'd leave us money for food shopping, which we mostly spent on chips and chocolate (and cigarettes
Not Envy). We'd have friends over at all hours, drank alcohol, tried cannabis, had dodgy 'friends of friends' turn up and expect to "join the party", boyfriends to sleep over etc. It led to us being much more adult than we should have been at those ages - I had to manage my 13 year olds emotions during a pregnancy scare (thankfully she wasn't). We were incredibly lucky to make it through those years relatively unscathed.
I now have a 14 year old DD (and a DD who is 12) and there is no way on earth I would leave her overnight. She's far more sensible than I ever was at her age, but I recall the terror of watching the house fill up with randoms, having no control over who was in your home and the pressure of trying to ensure your DSis felt safe - even when I didn't.
DH and I very occasionally go out for dinner in the evening and leave the girls at home together, but we always have a set time we will be home by and can always be home within 10 minutes if they call.
I suspect that my experiences as a child have made me a little stricter about this stuff than I would otherwise have been, but their my children - I just want them to be happy and safe, it's simply not worth taking the risk.