All settings are listed with their recommended values.
It's a hidden setting left from early openttd versions (was called "Deliver cargo to a station only when there is a demand"). If
off industry will deliver cargo to all nearby stations even if there is no vehicle picking it up. Don't think anyone needs an explanation why is that bad. If you have some suspicions of having it
off you can check that in config file or by typing
setting order.selectgoods in console.
TLDL; When it comes to dealing with breakdown stupid solutions work better than the smart ones so there is no point in enabling them.
The way breakdowns are implemented in OpenTTD they force you to build your networks in a very specific way. For example, at pretty much any point any train can choose to go to a nearest depot. So you have to make sure whenever it does so it can return to his route. That means building depots on every junction, station, etc. Also even if they're serviced regularly they still break down sometimes so you basically need to have lower train density than you would normally do. It all may sound ok to get working once but it starts to get annoying if you build a lot as instead of building new routes you waste time placing stupid depots and if you miss any you suddenly have trains stuck somewhere they don't belong. also something goal something (cb)...
realistic acceleration: on
Add nothing but exploits to the game.