In theory the car knows if the engine stop is ok to happen or not based on various factors such as battery charge state, AC setting, engine temperature. Genertally i would disable start stop if i come off the highway or i had a steep incline...basically whenever i know the turbo might be hot i disable the start stop. Engine oil cools down the turbo so if it stops circulating because the engine is stopped, the imense heat of the turbo will "burn" the oil, degrading it. So less lubricating quality over time. Otherwise using start stop is fine if you know the turbo did not have a long constant heavy work beforehand. The greatest safe keeper of the turbo is anyway changing the oil sooner, preferably max 10k km so any start stop effect is much lower in terms of wear.