When using 80mhz channels you have:
- Fewer non-overlapping channels so interference is more likely.
- Some clients that have packet aggregation issues that could affect performance
- WLAN infrastructures that rarely run 80mhz wide channels so bugs with 80mhz wide implementations are less likely to be seen or fixed.
- Throughput that can be affected by impairment on any of 4 channels.
- If you use DFS, the more likely the chance of false radar events to occur..
Long story short, there are quite a few things that could go wrong with 80mhz channels.