Tim of Gothridge Manor brings up some good points on the Sleep spell.
What I do in my S&W Majestic Wilderlands campaign is have the caster roll 4d4 for the hit dice effected with a max of 4HD . Allies of the caster are not affected. This results in up to a possible 4 4HD creature being affected. Which is a little more generous then by the book but I find it much easier to use in handling groups with varying HD. In such groups I count off the lower HD first.
Part of the problem Tim talk about is amplified by the fact that so much of my campaign takes places in cities and locales with a lots of people. Unlike a dungeon where the use of sleep becomes less and less the deeper you go the sleep spell remains a potent weapon in the Majestic Wilderlands throughout the character's career.
Tim's post raises some interesting points which our group will need to think about.
This is one of my house rules from when I ran 1E back in the 80s.
Warning, Kinda Gross
8 minutes ago