Thanks for this. Is there some further information to understand the gains and risks of setting/changing that?
The normal, safe and sound thing to do is to run in sync mode.
The async mode is only there because of special cases, and require special design. Come talk to us (me) if you think you have a use case in this category. An example might be that you have many standby nodes, for example. With synchronous mode you'll always be waiting for the slowest standby to respond (or timeout). Async mode removes that slowness, but this is unsafe from HA perspective unless special design measures are also taken.