I’ve had my A3’s for almost 25 years, and in the beginning, I always left them plugged in with the bias set to the threshold of “crackling”. Unfortunately, I also experienced many insulation breakdowns. Then I started turning the bias down after each listening session, and I haven’t had a single breakdown since.
I like leaving the bias on as the electric field repels dust, and cutting the bias voltage roughly in half dramatically reduces the stress on the insulation. Since I have a monoblock amplifier situated behind each speaker, I simply give each bias pot a clockwise twist after switching the amps on, and a counter-clockwise twist when I turn them off.
With hindsight I suspect that the breakdowns were probably caused by the very high output resistance (300Meg) of the original bias modules. On humid summer days I had to turn the bias way up to get the same effective stator voltage, so a drop in humidity resulted in the stator voltage increasing beyond the voltage rating of the insulation. I only figured this out years later out when Roger sent me different bias modules that had 10x lower output resistance (30Meg), so humidity is no longer a factor. However, I still reduce the bias between listening sessions to minimize the voltage stress on the insulation.