The problem is that the slower it is the more the window for error grows. And the harder it is to recover. It also impose a high boundary to latency. You cannot

The problem is that the slower it is the more the window for error grows. And the harder it is to recover. It also impose a high boundary to latency. You cannot be faster than your clock error without risks. Note that even Spanner had multiple downtime due to clock and/or network failures. In these case, any operation lal guarantees are lost. This makes it really dangerous.