anerobic soil

Just curious here. I hear people saying just use clay like soil for lilies
and not soil with contents which will break down. But I notice every year,
even if I only use cat litter by the next, this soil has gone stinky and
anerobic.

Lately in my local group I have heard advice to just use gravel when
possible, to keep if from going anerobic.

What is the detriment of having anerobic soil in a pot?

Thanks

Bill Brister - Austin, Texas