Kudos for asking this, as it shows you're being very thorough. The main, commonly spoken about disadvantages that OLED TVs have is the potential for screen burn-in (where pictures, artefacts, and outlines can still be seen on the screen long after it's been turned off), degradation over time, and a relatively higher price tag. However, especially in the most modern TVs, the burn-in is not really a problem that's proved to have an impact, the degradation over time is not unique to OLEDs as other screen types will, naturally, get weaker over time - but the cost factor is something that remains. Particularly on those higher-end Sony models, it's clear that some extra investment is required.