This s a party game and alot more companions and pets can get value out of that one turn of sleep but that 1 turn is one round for the gnoll(if he doesnt get shoved before his turn) or whatever the debuff spell may be...
But thats not it. the 'one turn of sleep for the gnoll' is down to half a turn of sleep /if he make next save) because the target gets a new save at start of next turn (he's initiative). One turn of sleep happens at Gale's inititive count.
Look at it from Gale's perspective. -I cast sleep on some target because they are many and we are few. If the miss their save they are out of the match until my next turn. My comrades can focus on other targets. YES! Those two Gnolls missed their save and are now a sleep. I am contributing to the party. Then half a turn later its Gnolls init count and they prematurely get a new save. If they make it then I have gained nothing. Maybe I should just be the Evoker every turn instead. Sure some in my party can get something out of it. But not all of it as ment in spell description. Its a combination of two botched things. Premature saves and the free-action-shove to automatic-standing-up.